Not attracted to guys anymore?

Im 18 years old now and I've found that I'm less and less attracted to guys. I used to be super boy-crazy, pointing out to my friends all the hot guys that I happened to have seen at work, at the grocery store, in my neighborhood that day etc. I've always been the same until now and I don't know why. I just don't want to be around guys in general, and all the ones in kind of hanging out with now, I like them, but I only really see them because I'm bored or have nothing to do that day which makes me feel guilty. I even considered I might be into girls, but once I got a proposition from a cute girl i know, the thought of it didn't seem so appealing to me anymore. I'm wondering if this is normal or if people have phases like this. I seriously have NO interest in men at this point. I haven't been in a serious relationship for over 6 months, so i don't think it's that I'm not ready to date or anything... whats wrong with me?