I'm not sure if I'm gay or not?

I've always seen my self as a straight man but now I'm 22 and I'm not sure. I've never had an erection to males nor have I ever masturbated to male porn. Since High School I've had plenty of sex with women and enjoyed it, and I still here "He's Gay" referred to me. So what I'd like to know is how does someone like my self figure out whether or not there gay.