Help me! I can't enjoy sex.

My boyfriend and I have been together for two years almost. We've always had great sex, and I've always gotten off every time. I'm not too hard to please. But lately it's been hurting down there. I get wet, but when he puts it in, it just feels uncomfortable and dry, even though it's not. I can't enjoy it because it hurts too much, and the only position that feels right is missionary... I don't know what to do. My sex drive has always been high, but I'm just not feeling it too much anymore because of this problem... Anyone have any advice? Please help! I love having sex, please please help! Lol