Could you have adhesion's or scar tissue? I've had chronic pain due to this and I remember it started with pain from movement. It was a pulling and tugging pain at first. Just a thought....
It could be a lot of things. Anything from a hernia to pregnancy. I don't want to freak you out or anything but it couldn't hurt to take a preg test to rule it out. Sometimes constipation and gas can cause pain as well. If it keeps up I would make an appt with your doctor.
We're not doctors here, just people dealing with Chronic Pain who support eachother and answer questions to the best of our knowlege.