Open Question: Stomach Problems I'm Having..?

I don't have a clue what this could be a sign of but Lately I have been having Problems with my stomach.. like one day these kids at school told me that I'm like fat but I'm only 115 and I'm almost 15 so that's around normal but i didn't take it that way and i tried to starve myself... well then i tried to eat again and i started feeling like every time i tried to eat i was going to throw up..