sex hurting

I definitely consider myself a nympho. I constantly want to have sex with my boyfriend no matter the time of day. Sometimes he isn't in the mood, but sometimes we will have sex like 3-4 times in a day. But I can't get wet like I use to be able to. So after awhile it starts to really hurt my vagina, but I really want the sex. How do I fix this?! I use lube, but that doesn't seem to help too much either.. I don't know how I can get myself wet again.