There can be many things that would contribute to an upset stomach. If it is bad, I would suggest that you see a doctor.
Nausea, Heartburn, Indigestion, Upset Stomach, Diarrhea.. one answer PEPTO!
Take some pepto.
If your tummy hurts, you should tell your parents or teacher. They will know how...
Try Drinking regular tea with freshly squeezed lemon or honey. Do not use sugar....
In Italian, it would translate to: "Le mie ferite del tummy". !