I've just come off the pill too, and am sexually active. My period was two weeks late recently, and i had some cramps that were not my usual type. Two negative pregnancy tests, and some worying later it finally arrived and things seem to have settled. The cramps you mention sound a bit bowel related considering the area. Try peppermint tea, and get some gaviscon or rennies and see if that settles it. It might be overproduction of stomach acid whcih I think can be stress related. To be honest though it's worth a trip to the GP just for peace of mind if nothing else.