What should I do? Helppp?

I'm a 15 year old girl. I can't stop hateing myself. I feel so fat and gross all the time. And I've been extra sick because I have IBS and Lactose Intolerance so far. They'll probs find something else wrong with me. Everyone else is like a size 2 or 4. and I'm like a 7. Sometimes I'll look at myself and actually think I look good. Then I go out in public and see other people and then that confidence just dies. I play sports and everything. I'm athletic, but I feel too muscular. and I'm like super short. 4'10 1/2. :l so that doesn't help. I have a boyrfriend, but I feel like he doesn't even like care about my feelings about this. I feel like he'd leave me for some skinny girl any day. The doctor told me to just lose 10+ pounds and I'll be good, but whenever i lose, I just gain it back really quick. And everything i eat makes me sick. So I hate eating, but i love it at the same time. What should i do? I've tried telling my family but all they say is just lose weight so I can be like everyone else.... Who says that? ugh. Help.