What's wrong with my bladder?

I constantly feel like I have to pee and when I do, it's only a little bit. Right at the very end of peeing I suddenly get this horribly uncomfortable feeling like my bladder is being pulled on or something. It isn't necessarily burning or stinging and there isn't any blood, it's just this weird feeling. I haven't looked yet to see if I'm red down there or anything. But, have you felt this before? What is it?