Better orgasm with a full bladder?

I've always been able to achieve a better/quicker orgasm with a fuller bladder, and I have no idea why, since I didn't know the urethra affected stuff like that. Is this normal or does that mean somethings wrong with me? I can't really come when I'm having sex with my boyfriend and I'm beginning to think its because I always empty my bladder before hand, for fear of having an accident. It does seem like when I haven't, I get closer, but I stop because I end up feeling like I have to go.