Pain during sex (maybe tmi)

When we do it From behind, it hurts. Not to the point where I stop. I always let him finish, but it still hurts. Or if im on top, sometimes it'll hurt. Im always wet and wanting it. He's not like extremely big so its not that either.. 
I dont have insurance right now for a doctor but im confused. We also have been ttc for 2 years no luck.