What does a missed period mean? Am I pregnant?

Me and my boyfriend had sex, we both lost our virginity to each other he stuck it in without a condom at first then he took it out, put a condom on and used it for the rest of the sexual intercourse i'm scared of maybe some kind of pre-ejaculation getting me pregnant, its been 2 weeks since we had sex and i was supposed to have my period ten days ago so im going to wait for my next period , does this mean i'm pregnant?? please help!