A really bad diet... possibly anorexia?

Hi, i'm 15, 5"4 and 110 pounds. For the past two years I have rarely eaten a full meal a day if even that. It's not because of financial circumstances. I was admitted into the hospital last summer due to severe iron deficiency and a hemoglobin at 5. The doctors said a normal blood count for my age is 12. I had to get a blood transfusion. The doctors said a lot of the reason why I was in such a critical condition was because I wasn't getting any of my nutrients. After being hospitalized, I started eating more regularly. At the time I was less than 100 pounds. Because of the sudden change in diet, I gained weight rapidly, which I realize is healthy. However, it was really hard for me to accept gaining weight. In fact, I still haven't accepted it. My poor eating habits started to come back a couple months after the transfusion and I have tried losing weight. I know that I am at a good weight, but after being so skinny for so long has made it extremely difficult to accept being this. I am scared of gaining weight because I am surrounded by extremely thin family members. They all eat a lot more than I do, but somehow my sisters manage not to gain any weight. I guess I realize that I have a problem, but I don't know how to fix it without gaining a lot of weight. I go through periods where I eat normally, but recently, I have started worrying more and more about my size and i've started to eat a lot less. Any advice? Thanks in advance.