Ok aside from my wierd topic title

...
heres the thing, whenever me and my b/f have sex...its fine and dandy but on occasion like when i am ontop it kind of hurts when he gets in me,.And when i go to the bathroom, it burns...almost like the skin towards the back has been rubbed raw (sorry if that was kinda grusome). I don't know what it is, but it stings like none other... i was thinkin that mayb i'm not wet enough before hand? i dunno! any help would be appreciated!
Anette0513