Calories, metabolism, other things. Please help!

Well hello,

As you can see, this is my first post. I don't really use MFP so I don't have an eating journal. I really need some guidance on my situation. Is a long post so bear with me. I am 19, female, 5'4, 127 pounds. I have been struggling with my weight for about 3 years now. I am what some would call "curvy" but not fat. From when I was little, I used to be able to eat anything without really gaining weight. I also did not care about my appearance until I reached about 15. I then started to watch a little mroe what I ate but I still ate all my meals and played sports. I now eat just a 1,000 calories a day otherwise, I gain weight. From Jan to April, I went down to 112 pounds. People called me all sort of names, saying my figure looked horrible because I have big, muscly legs, anorexic, etc. In May, I decided to gain back to my previous weight because everyone said I looked my best. Now I am back at 127. However, I am always starving. I have always been one to eat enough leaning towards the "a lot" side. My stomach growls all the time. But if I eat even a little bit over, I gain weight. I am also salt sensitive. So if I eat too much salt for a day, I've been able to even gain 8 pounds of water weight in a day. Those do come off a few days later. Anyways, I recently had my thyroid tested, and my levels have ranged from 35 to 47 in the past few years. That's hyperthyroidism. However, I gain weight easily, do not have rapid heart beat, but I do suffer from insomnia, I'm always moody, weak, and tired. So basically my symptoms contrast each other. I don't know what to think. I've been depressed due to this eating lifestyle. I cannot fathom my inability to be able to eat more. I've been able to eat 15,000 calories in a day. That's how hungry I always am. I can eat a full plate now, and an hour later, I'm hungry. I've tried lifting my protein intake, eating more greens, but nothing fills me up. By 1:00 pm, I have usually eaten all my day's calories worth. It truly is frustrating. I work out about 5 times a week. Try to vary with cardio, strength training, etc. I've read all the info on the "starvation mode" and whatnot. I also do eat back my workout calories so, somedays I eat 1200. I've been slowly binging these past few days and can't stop due to hunger. It's not anxiety or emotional. I've tried drinking a glass of water before food, and confuse my stomach and see if its just anxiety, but no. Growls, empty stomach pains is all I get. I've read is common for people who undereat for their stomachs to shrink with time. Mine, the less I eat, the more it expands. My body is so confusing. I don't know what to do. I've done so much research, it's all confusing. Any advice here? Ahh I forgot to mention, I had my BMR tested and it is 1050. I'd like to know how can I lose 5 pounds with only eating 1000 calories. I cannot lower it, otherwise I probably wouldn't function. Any suggestions on why my body behaves this way? Any advice is greatly appreciated. thank you.