Eating Disorder?

Hi, Im 15, weigh 47kg (103 pounds) and am about 163cm. I have a athletic body, and im worried that i might be getting a eating disorder. My mum says its just how im built, and i'll get better. First of all, im scared to gain weight, and go over 50kg. I know im growing, but i dont wont to gain weight. I dont eat breakfast, sometimes lunch, and mabey dinner. I weigh myself, and if i think im getting close to 50kg, i wont eat, and might do some exercise. I have also found myself looking at lables on food, to see the fat content.
Help me please!!!!

[cyber_furby]

also, i have a low self esteem from some 'friends' calling me anorexic, because of a photo you can see my ribs in. *sigh*

[PenelopeAnn]

Some people are slim, some are not. As you grow your body is going to change. You probably won't come into your mature, woman body until you are in your early twenties. My  questions-

Did these behaviors come before or after your friends made these comments? Sometimes, when someone is making comments inaccurately, it can affect in a way where you start fulfilling their ideas of you. For example, some girls who get a reputation for being sexually promiscuous when they aren't, they might go out and become that with the idea of - if I'm going to be accused of it, I might as well be it. Are these friends verbalizing something out of concern? Or do they have unrelated issue with you and just found something they could give you grief about?

I think you need to answer those questions before you can get a clear idea of what is happening. Sometimes, people will make jokes or razz you about something in a lighthearted way, but in truth, they are worried and cannot figure out how to approach with such serious concerns. It is normal for a girl your age to worry about their body and how other people perceive it, but some of your behaviors could have the potential to grow over time. Do you have a health teacher at your school? A coach or counselor? I would talk to them, because they will most likely have some information and education on eating disorders.