Re: Weight Gain.
I had to eat 1200 calories a day in the past to lose weight since I was already at a healthy weight. Now that I am a bit more active (I used to work out 30-45 minutes and now I work out more like an hour or more), I can eat more. It's hard to tell exactly how many calories you need, but you can try adding and seeing if it makes a difference for you. I had a nutritionist that helped me determine how many I need. At first she had me at 1500 but I wasn't losing so we had to drop down to 1200. Unfortunately, sometimes it's just trial and error.
What you are eating does make a huge difference. I used to eat "healthy" snacks like 100 calorie packs and things like that, but now that I stopped eating those so often, I feel better. I also stopped eating so many Lean Cuisines and lost weight. Those are pretty high in sodium, which can cause you to store water weight. I'd try drinking plenty of water these next few days if you feel bloated or even some green tea (one without calories or very few). But if you haven't changed anything, likely it is just water weight from something you ate or drank. Just try to eat very clean right now (lots of fruits and veggies, less processed foods), plenty of water, etc. and hopefully the weight should come back off.