Someone else who needs help.

I've always lurked in this community (among others) but you guys are very friendly and I need some advice or encouragement or something right now. I'm not sure what. Here goes: I am a person who has never been able to eat much. I was obese for most of my teen years because of this. I only ate once or twice a day (if I remembered) and it usually wasn't something particularly healthy. I was always curious as to why I was so overweight when my friends would be eating but I just couldn't bring myself to. In college I became a very active runner and I lost weight pretty quickly (around 3 kg/5-8lbs a month) and eventually hit my goal of a healthy BMI. Over the past year I noticed myself becoming increasingly sedentary and wanted to drop to my ideal weight. Since April 1 I have run at a minimum of 5k at least 6 days a week. However, I've fallen back into my trap of only snacking on veggies, nuts, and pretzels and forgetting to eat. I don't binge, but I do occasionally eat something I regret (like a few pieces of pizza or spaghetti). I have gained around 5 pounds since then. I'm very, very upset. I understand that my under 1k daily calorie consumption is possibly crashing my metabolism, but the idea of eating more already upsets my stomach. I decided to start weight lifting for a half an hour every other day instead of running to possibly make me hungrier or at least try to get rid of my cardio flab, but I'm scared of gaining more weight.

It could also be water weight, but why would I gain 5 pounds of water weight steadily over a month after starting a strict cardio regime? I've been drinking probably a gallon of water a day to stay hydrated, but I weigh myself in the morning.