Is it normal that i can't orgasm?

So I'm a fairly attractive, young, college student, 18 years old, and I've never achieved an orgasm, even on my own. I've had about 6 or 7 partners in the last 3 years, some of which were very "skilled" in bed, some started as virgins, a few I've loved very deeply, but no matter how long we go, how hard, how soft, i never quite get "there."
i mean, its still enjoyable, but I'm just wondering how much longer I have to wait, what (or who) i have to do to finally enjoy sex to the fullest.