Am i too fat?

im 13 years old im not over weight. but i think i kinda am i weigh about 100 pounds i wear a size 1-3 in pants and i think im kinda fat because there are adults who wear the same size pants as i do so i must be kinda fat and i dont want to imagine how fat ill be in the future.when i eat i try to purge my food out and that didnt help so now i eat once a day which is usually a couple of saltine crackers and thats about it.and nichole richie weighs 83 pounds and shes like in her 20s and im 13 and weigh like 100 pounds i wanna know if im too fat?