Gym 5 days a week, but I'm GAINING weight?!

your most likely gaining muscle, do you do measurements?

are you consuming a lot of sodium? Your body retains water when you work out to help repair your muscles... You might have to change it up. I rarely had this problem tho -- i dunno. I don't eat any of my exercise calories back -- sometimes i do end up using some of my exercise calories up when i go over but very rarely

^^^ Ehhh, probably not. It takes a lot to gain a pound of muscle. A LOT.
My suggestion is maybe it's your muscles retaining water. If you are working them really hard, they may be holding on to it. Just keep doing what you're doing.

My first 6 weeks at the gym I was eating like a saint and going 6 days a week burning heaps of calories but hardly losing anything. I was getting really deflated and then I measured my waist and found I had lost 8 cms. WOW! Now I do not put so much emphasis on the scales and use a few methods to measure whether or not i am having success.

You also have to be careful that you aren't rewarding yourself with food because you are exercising regularly ie. "I'm going to eat that treat because i did xyz at the gym today".

Stick with it and you will start to see results that are much more satisfying then what the scales will give you:)

Definitely NOT muscle gain after only one month. Muscles may hold more fluid after intense exercise, but that's not increase per se.

You say you look like you're slimming down? Have you taken measurements? you know like waist, hips, chest, thigh? Have they changed?

If you're loving the gym, then go for it, at the very least, you'll be getting much fitter and healthier. You might need to tweek your diet abit, have a look at the NIH site for weight loss or the Mayo Clinic site for some different ideas.

If you're going to the gym 5 days a week, and only eating back half of the calories per exercise, I would then ask what exercises you are doing.
Are you doing cardiovascular or strength exercises? Although weights training does use up calories, they make you gain muscle mass in the process and muddle up the figures.

My advice? Try a week of light cardio only and test the results. If you pull a 1-2km run a day, I believe you'll see a significant change.

And assess your goals - which is more important to you right now: do you want to lose weight or gain muscle mass? You can do both, but you'll be gaining weight as you see here.

As a point of reference, I go to the gym three times a week:
I run once a week (5km run at 10km/p/h).
I do weights the other two days, about 45 mins of chest/biceps/shoulders.

With this type of workout, I see an average loss of 1kg a week. Every body is different, but why not try to change you're routine and test the results?

Under the best of conditions, you can typically only gain 2 pounds a month of muscle. And that takes effort.

What is probably happening is your body is retaining more water because of your increased activity. If going to the gym 5 days a week is a new thing, your muscles are having to do a lot of tiny little repairs to themselves and they need the water to get it all done. Once you settle into the routine and your body is used to that level of activity, the water weight will probably drop. In the mean time, like others are suggesting, start taking measurements. If you are losing inches but gaining weight, it is almost certainly water you are gaining, while also losing fat.

I also read an article a while back that said when you lose fat your body will sometimes fill the fat cells with water temporarily, because your body doesn't believe you will keep losing weight and wants to save the space for fat to come back. After a while your body will figure out you aren't going to be gaining anymore fat and start to let that water go. I can't find the link now but will post it here if I do.

The number on the scale isn't the only thing that matters, you know what you are doing is good for you so stick with it!

You should add sodium to your diary. And drinks lots of water. I would suggest trying to even out your meals more maybe. Almost nothing for lunch and a lot at dinner. The bigger meal might want to be earlier in the day.

I know EXACTLY WHAT YOUR GOING THROUGH, AND IT SUCKS. Lol well it doesn't suck because I am actually leaning out and gaining muscle, but literally the scale has only gone down 4lbs in the last two months. I am DEFF. more toned, especially my arms and legs! When I tell people how much I weigh they're suprised. ANYWAYS. I have decided to not look at the scale anymore. It is way too discouraging, I am going by how my clothes fit and how I feel. But that stupid scale is always there in the back of my head! Anyways, my trainer has too told me to stop weighing myself because it is so discouraging. I think we put too much one weight! If there is someone who is 200lbs of fat, and 200lbs of muscle obviously ther person who weighs 200lbs of muscle is going to look way more fit! soooo screw the scale! Go by how you feel! or maybe just weigh yourself once a month? As for me I have decided to just stop weighing myself completely until I feel confident enough to put a bakini on...... And even then I might not just because that stupid number can have so much power over me!