I think you should change your eating habits and see if there's a difference, be active as well
It can be hormonal, i don't know if you reached puberty or not .. But hormones can affects, espacially girls and women, start with the obvious thing which is trying to eat healthy, if you don't have appetite at least eat 3 big meals a day, meals that should offer you various nutrients, meals which are balanced and surly unprossesed .