I am 13 years old and weigh at a size of 169cm only 44.1 Kg. In addition, it is often so that I in the evening after eating 600g more weigh than the next morning. Because of my weight I are also quite a few pants and bikini I see anyway of not nice, because my shoulders are so bony :(
The best answer
since you are only 13, I would seek no means any unilateral and greasy food!
I even think many girls your age, it goes like this. With time and the age vorranschreitendem the perspective most.
Otherwise: You Eating because sufficient? How much you move?
In no event fast food :) just try every day to take 3 regular meals. But a piece Schocki has not hurt anybody!
More greasy food and eat candy and operate less sport. So you would have to be thicker. take => More calories than you consume.