It feels sore and it hurts really bad sitting or trying to sit and standing

Good evening.

Have you told your parents that you are feeling ill?

It is possible you are in the early stages of Appendicitis. It would be best to get your parents to take you to a doctor now.

There's so many things it could be in the abdomen.
Slow appendicitis, gallstones, ulcer, ovarian cyst, or just some sort of indigestion, poor diet, or food allergy. Stress and worry. Pregnancy.
Some less common ones and some very uncommon ones too.
Tell a parent, take your temp, call a doctor!
Even appendicitis can get very serious very fast.

So that you are not absolutetly terrified by the other answers *hehe love you guys*

I would also like to suggest that it could simply be menstral cramping. Some girls get them VERY VERY BADLY, to the point of incapacitation.

Either way, I stand by the others comments. Talk to your parents and go see a doctor!