why don't i have an interest in sex?

i'm 15 and i've had sex a few times but i just don't see the hype of it. everytime i've never had an orgasm (even though i'm not exactly sure what that's like i think). its only with other people. when i masturbate it feels so good and i'm not exactly sure what an orgasm is but if i've had one its been while masurbating. and then it gets awkward bc he'll be done but i won't because i don't know when to "be done". help