I'm hungry all the time, and gaining.

1) Drink more water.

2) Get to a doctor if you can. (This happened to me, and it turned out I was preggers.)

Your hormones can be out of whack at any age... PCOS is an example of having hormonal imbalance. I'm sure there's plenty of women who have no idea that they suffer from it. As several people suggested here, you should seek a physician's advice because, honestly, that's the only way you're going to find out if there's something physically out of whack with your body. Your doctor will recommend a dietician or nutritionist as well.

Also human body doesn't know what is "clean" diet.

Of course it does! It's called HEALTH.

Taken from someone elses post - very helpful:

This was a BBC programme first shown earlier this year and repeated on one of the Sky lifestyle channels this week. I missed it the first time, so I apologise if it has been discussed on this forum before, but I thought it was really interesting and I believe it may still be available to view on iPlayer for those in the UK.

The following is a synopsis of the programme which I have found on another forum:

1) Don't skip breakfast

I think this one is well known, but this showed a different reason. The man being studied had brain scans when presented with pictures of food in two different conditions.
The first condition was with a full breakfast, and when shown pictures of both low and high calorie food, the part of the brain controlling appetite (hypothalamus I think??) didn't produce much activity.
In the second condition, with no breakfast, the same part of the brain lit up much more when presented with high calorie foods, meaning that we subconsciously crave the high calorie foods, which could make up for the skipped breakfast or go over it in terms of calories.

2) Change to smaller plates (portions)

A study was done on two groups of people watching a movie. One group was presented with a large bucket of popcorn, and the other group with a smaller bucket of popcorn.
Both buckets were big enough so that the participants could eat their fill and still have a lot remaining; nobody finished the popcorn.
However the results showed that the group with larger buckets consumed on average a 33% more popcorn.
Reducing the dish (plate/bowl) size could significantly lower the amount you'll eat.

3) Count your calories

A lot of things are overlooked on diets, such as drinks, snacks & even healthy foods.
A radio DJ who was over weight and had been on a healthy diet for 5 years with no result but she did not count calories.
She was put on a video diary, and then a written diary for 9 days. But at the same time she had to drink special water with chemical isotopes that could tell how many calories have been consumed & burned.
In her diaries, she recorded eating only 1100 calories because she under-counted calories from her breakfast, a hearty fruit salad, but was 500 calories on its own. The results from the isotopes found that she had in fact been eating 3000 calories (undercounting by almost 66%), and this brought to light the fact that many people miss out many calories such as juices, fruity snacks or other sorts of snacks that are healthy but still count towards total calories.

4) Don't blame your metabolism

The same woman from above stated that she couldn't lose weight because of a slow metabolism, but however she had a near spot on average metabolism. The weight gaining could be blamed on the amount she was eating rather than what, and so she was simply overeating.

5) Protein staves off hunger pangs

Carbohydrates stimulate the production of PYY hormone to the brain, which signals more hunger pangs.
Protein, however suppresses this and so stimulus of being hungry is no longer sent to the brain and so why the satiating effect of protein.
A group of bridge painters were tested. They were given exactly the same breakfasts in terms of calories, but one set was given high carb, the other high fat and the other high protein. They were given pocket computers to rate their hunger on the hour every hour. The results showed that the high carb felt hungrier, whereas the high protein felt more content and less hungry. The high fat was in the middle.
So if you want a filling breakfast, add the protein in,

6) Soup keeps you fuller for longer

Hunger pangs are caused by the stomach shrinking after it has been emptied of food.
Two groups of army trainees were given the same, exact food and the same amount. Chicken, rice, carrots, peas and a glass of water. The yellow group ate this normally on a plate.
However, the red group had their food & water blended into a soup.
An hour after the meal, the groups' stomachs were scanned using an ultrasound scanner to see how big the stomach was. At one hour, the yellow groups' stomach was already 60% the size it was at the beginning, but the red team's was at 90%.
At 2 hours, the yellow team's was at 40%, the red group still at 70%.
At 3 hours, the yellow groups' was empty, but the red team's was at 40%.
Finally after 4 hours, is when the red teams' stomachs were finally empty.

The results showed that the soup stayed in the stomachs for longer, due to the water being blended in and not being able to drain, because as it drains, it leaves the less space-occupying solid food, which is what occurred in the yellow groups' stomachs. This means soup can stave off hunger for at least an hour longer due to the fact the stomach is still occupied for that much longer.

7) The wider the choice of food, the more you will eat

Two bowls of sweets were left in a cafe during a lunch break for staff. One bowl contained multi-coloured smarties, and the other contained purple smarties only. They were labelled free sweets and were left for the duration of the lunch.
The results were that all the multi-coloured smarties were eaten, whereas the purple coloured sweets still had half left in the bowl at the end. The conclusion was that we tend to eat more when there is variety than when there isn't. This is due to inherited instincts from our hunter-gatherer past (and also the fact we need different nutrients from different food sources).
They highlighted the fact that when there's a lot of variety to choose from, we eat more. E.g. buffets we eat a lot more, almost 3 times as much as we would eat in the house. They stated if on a diet, try keep the amount of food you have available to eat a minimum in order to not "feel like this food" or "feel like that food".

8) Low fat diary can you help absorb less fat from food

The calcium in dairy products binds with fat to produce a soapy substance that gets excreted because we cannot absorb it.
The bassist from blur was tested for this hypothesis (as something for the TV, obviously large scale testing has gone on prior to this). He had his diet planned out by professionals and so ate the same macros, except the first week was low dairy and the second was high dairy. He would then collect a sample of his faeces and send them off to a lab for testing, to be averaged for the week.
The week with low dairy had 1.5 grams of fat per 100grams of faeces, and with the high dairy week he had excreted an average of 3.09 grams of fat per 100grams of faeces.
If he was to carry on the diet without making any changes to macros, he would excrete an extra 2kg of fat a year.

9) Exercise - fat continues to burn after you exercise and even when you sleep

I found this one quite interesting because it involved steady-state cardio rather than high intensity.
Again, it had been done in mass studies but this one tested the presenter of the show for real-life purposes.
The presenter never did much exercise, and so was tested one morning for how much fat he burned for a base rate.
He was then asked to do brisk walking, not too strenuous, for 90 minutes. He burned 19 grams of fat during this session. However, overnight, he burned an extra 49 grams because of the after burn. This is because, as the glycogen in the muscles was depleted, the body had to use a different fuel for not-so-strenuous tasks like just living, and in this case, fat.
It takes up to 22-24 hours for the body to replenish glycogen in muscles, and in this time after an exercise session, it uses up fat stores instead.

10) Small changes in daily routine helps lose weight

This one, again, obvious, but the same woman who was counting her calories before was followed during her daily schedule. She would sit down mostly, making phone calls and using her laptop before commuting to London for lunch via tube trains & using the escalator, then going to a knitting shop & then onto her 2 hour radio show sitting down.
Her heart rate was measured and plotted on a graph compared to the movement she was doing (she had a motion sensor & a heart monitor).
On her normal days, her heart rate only went up 3-4 times in a day because those would be the times of activity (commuting, etc).
She was then asked to do more moving around in her daily routine, such as moving about when on the phone, walking up and down the stairs more when doing housework, getting off at a later or earlier stop and then walking the distance for lunch, climbing the stairs instead of using the escalator, and doing air-aerobics at the radio show, and the results were that there was more movement, and a higher heart rate. She burned an extra 240 calories to the week before and her heart rate fluctuated much more.
Small changes to lifestyle can increase the amount of calories you burn by a significant amount.

9) Exercise - fat continues to burn after you exercise and even when you sleep

I found this one quite interesting because it involved steady-state cardio rather than high intensity.
Again, it had been done in mass studies but this one tested the presenter of the show for real-life purposes.
The presenter never did much exercise, and so was tested one morning for how much fat he burned for a base rate.
He was then asked to do brisk walking, not too strenuous, for 90 minutes. He burned 19 grams of fat during this session. However, overnight, he burned an extra 49 grams because of the after burn. This is because, as the glycogen in the muscles was depleted, the body had to use a different fuel for not-so-strenuous tasks like just living, and in this case, fat.
It takes up to 22-24 hours for the body to replenish glycogen in muscles, and in this time after an exercise session, it uses up fat stores instead.

I found this interesting and will definitely keep this in mind!

Eat a lot of slow-digestion carbs. So a lot of veggies like all the time. Constantly grazing. Also, you might be confusing hungriness with boredom or thirst. Make sure you chug water like all the time.