Bad cramps please help :(?

Hi there, I have been having this problem for about three weeks now which is bad cramps that feel like period cramps but without period. I get them when I have to pee and when Im finished peeing it's gone. Sometimes I get it when I don't have to pee and stand up quickly or walk but never when I lie down or sit. I have also been having diarrhea for about three weeks. I took two pregnancy tests and they were both negative. Could this have anything to do with the birth control pill yasmin? I've been taking it for a month. Please help :(