Is it normal to not know your sexuality?

I'm a sixteen year-old male and for most of my life I've thought of myself as straight, but relatively recently I've started wondering if I'm bisexual, or even pan-sexual. I don't see guys in the same way as I do girls, but I've sort of got this nagging feeling that's telling me I'm not straight. Is this quite a common thing, and is there anything I can do to tell my sexuality to stop being so Goddarn indecisive?
I'm kind of an introvert, and haven't had a proper relationship with either sex, so I don't know what those things feel like.