Pain after sex

Every time I finish having sex with my boyfriend I always get pain when peeing, and this could be straight after or the next day or even a few days later, I've been to the doctors thinking its a urine infection, but it never is, I have also been tested for STI's since I don't use a condom. It get so bad I sometimes pee myself because I can't control my bladder. However I use to get this pain all the time when I was only 8/9 so maybe it's nothing to do with sex.