Abdominal problem! please help! 10 points to best answer!?

ok im a 13 year old girl. for two months, i have had abdominal pain on the right side near my belly on. its a constant pain, and it hurts a LOT when you press on it. it got so bad the other day i couldnt even walk. i went to the ER twice and they did an Ultra Sound, a CT scan, took blood, and did numerous xRays and everything came back negative. i got a colonoscopy and an endoscopy and that was all negative. i also lost 10 pounds unintentionally. what could it possibly be? what are they going to do next? by the way i have my period and it isnt cramps because they feel different. also my doc is making me go to a gynecologist on wednesday, but i doubt theyll find anything.