I have a pain in my lower abdomen on the right side and my tubes are tied and I missed a period. ?

I'm not sure exactly what this pain is. It's not a constant thing. It gets worse web I move around and before and after I urinate. It doesn't move around or anything and I am worried that maybe it might be an eptopic pregnancy or perhaps appendicitis. Can anyone shed some light on this for me concerning what this might be?