No libido drive?? Why?

I've been dating my guy for 2.5 years. We had such a healthy sex life about a year ago. Now I don't know why by my sex drive is gone. I don't get attracted to anything. Other guys, master bating, porn. Nothing. I'm not on birth control anymore. I'm not that stressed, and my boy and I have a pretty good relationship otherwise. I'm only 23 years old...I should be at my sexual prime...any ideas?