Am i gay/bisexual???

ok so ever since i've been 11 i've been crazy about girls, like from 11-13 i used to go for preppy blonde girls, and from 13-16 more intellectual womanly girls, and 16-17 just weird girls lol. i've never actually thought about a guy before. and btw i actually have never gone out or done anything with a girl b4, i'm sort of nerdy and never had a chance with a girl b4, and i got tired of girls for like a few months and decided to just stop trying so hard for one since they were all being bitchess all the time and stuff, so...anyways right now i'm 17 and i think i have sort of a crush on this one guy. i have never been against gays etc, but b4 it repulsed me to think about myself with a guy, but i never actually pictured or tried having fantasies about guys. but now i sort of thought about him at nights, and got bonerrs etc. and now when i think of guys i actually kind of do feel attracted to some of them, like the thin emo kinds, but not the big football player kinds so idk. and it just randomly happened, like i thought about having sex and a relationship with him and all, is it just my pschology or am i bisexual? thanks