Guide to calorie deficits

So now we can figure out where your goal should be.
Go to the tools section and figure out your BMI:

Generally someone with a BMI over 32 can do a 1000 calorie a day (2 lbs a week) deficit
With a BMI of 30 to 32 a deficit of 750 calories is generally correct (about 1.5 lbs a week)
With a BMI of 28 to 30 a deficit of 500 calories is about right (about 1 lb a week)
With a BMI of 26 to 28 a deficit of about 300 calories is perfect (about 1/2 lb a week)
and below 26... well this is where we get fuzzy. See now you're no longer talking about being overweight, so while it's still ok to have a small deficit, you really should shift your focus more towards muscle tone, and reducing fat. This means is EXTRA important to eat your exercise calories as your body needs to KNOW it's ok to burn fat stores, and the only way it will know is if you keep giving it the calories it needs to not enter the famine response (starvation mode)

So with my BMI being 27.2, it says I should only be shooting to lose 1/2 lb a week. Gosh that seems like such a small amount. You are saying if I bump up my weekly weightloss goal and my calorie intake goes down, I won't lose?

having a BMI of 27 means you probably don't have a ton of weight to lose (without looking I'd guess your goal is probably somewhere near 20 to 30 lbs or so? Depending on your height.). I'm not saying you won't lose with a larger deficit, I'm saying that it's probable that you're going to be very difficult to lose at a much faster rate than that, even if you raise your deficit, and in all likelihood, you'll lose at least some of that weight as lean body mass (muscle and lean tissue) which is bad, we don't want to lose muscle.

I am wondering if I must've usually been in 'starvation mode' because recently I've been trying really hard to actually eat all of my calories (hardly ever was before) and I've gained weight. It's not that I necessarily feel bigger but it's certainly showing on the scales. My instinctive reaction is to restrict majorly but clearly that doesn't work. So are you saying this gain is probably temporary as my body settles into what it should be operating in? It's just also that I run (starting to train for a marathon) and I do other cross-training too and sometimes I don't seem to be able to eat all my calories. True I'm definitely hungry but I feel like I'm eating heaps, especially compared to the people around me. I don't want people thinking I eat huge amounts. But like today, I burnt 846 calories running before breakfast, and I can't seem to make them up! I honestly have such a fear of eating all my calories because I am so afraid to trust that this weight gain is temporary.

Well, I won't really comment on whether you were in starvation mode or not as I have no idea about your stats. But I will say that it takes time for the body to recover from a fasting state, when in that state the body puts an emphasis on fat storage, and remember, when you are in a fasting state, the amount of calories your body needs to stay where it is (homeostasis) has been reduced because it perceived the true (meaning a deficit that it can't make up via fat conversion and protein conversion along with ingested calories) energy intake (food you eat) at being to low. Therefore, in order to "reset" your maintenance calories back to where they should be, you need to consistently eat enough for a few weeks at least. While you are resetting your body, there is a chance that you will gain a few lbs. It depends on your individual body whether this happens and to what extent, and it also depends on how quickly and how much you raise your calories. The slower you do it, the less likely it is you will gain weight doing it. Once your TDEE (Total Daily Energy Expenditure) is back up to where it needs to be, you'll stop gaining, and you'll probably also notice increased energy levels, increased abilities with regards to exercise, and overall more alertness and better outward appearance (skin, hair, nails, coordination, and also a better immune system which means less colds and minor infections).

I will caution everyone that each of us is in a unique situation, and our bodies all react differently within certain guidelines. So what may take 1 person two weeks, may take another 6 days. While 1 person may gain 4 or 5 lbs, another may lose weight. It's all a complex calculation involving chemical output, hormones, genetics, age, sex, weight, height, body fat levels, and physical attributes. So just because I give a timeline, doesn't mean you'll conform to it exactly, I generally talk in averages simply because I can't speak to each person individually.

Generally someone with a BMI over 32 can do a 1000 calorie a day (2 lbs a week) deficit
With a BMI of 30 to 32 a deficit of 750 calories is generally correct (about 1.5 lbs a week)
With a BMI of 28 to 30 a deficit of 500 calories is about right (about 1 lb a week)
With a BMI of 26 to 28 a deficit of about 300 calories is perfect (about 1/2 lb a week)
and below 26... well this is where we get fuzzy. See now you're no longer talking about being overweight, so while it's still ok to have a small deficit, you really should shift your focus more towards muscle tone, and reducing fat. This means is EXTRA important to eat your exercise calories as your body needs to KNOW it's ok to burn fat stores, and the only way it will know is if you keep giving it the calories it needs to not enter the famine response (starvation mode)