It could be your gallbladder. Even if you don't have gallstones. There are those of us who have had there gallbladders go bad without any gallstones. Ask for an U/S or Hida Scan..
It could be gallstone pain? I just had mine out so I am pretty familiar with this stuff!! My symptoms were mostly heartburn, but I did have pain in my upper right side also. Try this... don't eat any fat for a couple of days and see if it goes away. That was how I knew for sure... eating any fat would really hurt (within 5 minutes of eating).
Your doctor should do an ultrasound to rule gallstones out...
Good luck!!