What Causes Pain In Lower Right Side Of Abdomen?

I have a pain in the lower right side of my abdomen It just started a few days ago. However for a few months now I have been getting a cramp/spasm on the right side of my upper abdomen. It feels like its filling up with air and is very painful then all of a sudden it pops and goes away. When I bend down to tie my shoe it will start or when I get into the car and lean over to the side it starts I have to stretch my abdomen or lean far back for it to subside. I don t get this as frequently as now I have pain in my right side it even burns a little. What is this?