What causes pain in the upper right abdomen? I don't have the pain all the time, just sometimes. But when it hurts, it hurts bad. It is worsened when I do physical activity, but can start when just sitting. It also hurts more if I push on spot where hurts. Any help, please? Thanks!

There are two things there that could be causing pain. Liver and gallbladder. I am sure there are many other thing there that can cause pain but those two do create lots of peoples troubles. Both need to be checked out.

Find answers to your questions with this helpful reference about Liver pain - Causes and symptoms of liver pain

Sounds like gallbladder to me. You might not have stones but it can still be your gallbladder.