This is very akward for.me to post but I need some help insight or something...

At least twice that I know of my boyfriend has rubbed himself raw when we have had sex (think almost like a sunburn...that first thin layer rubbed off and about the size of a nickle usually) . I'm plenty wet and we have used lube. But aside from that at the same time it feels like he either stretches me to far or goes in at a odd angle (his favorite position is me laying in front of him my back to his chest) something...because it hurts for a few days afterwards. Almost like a tear or something but it's not? What exactly could we do to prevent this stuff from happening? What could be causing it?

Edit:He was a virgin before he got with me. He has no STDs. I also am clean. This rubbed raw has only happened twice in the 7months we have been together. It's always after rough sex.