Couple of things to consider: 1. Is it off to the side, like towards an ovary? If you are in the middle of your cycle (between periods), it could be pain from ovulation. 2. Or does it feel like youre sitting on a football? Thats what a bladder infection feels like to me.

Eta 3. It could be endometriosis. I felt like i was a vampire with a spike thru my gut! Not fun. My gyn said it could be just a microscopic bit of tissue stuck on a nerve, but where it doesnt belong.