If i have a period does that mean i'm not pregnant even though i had sex 2 days before i came on?

Yes: If you have a period, the you are not pregnant. Not all vaginal bleeding is the menstrual period. If a woman conceives implantation bleeding is common. That would usually happen about when the period is due, so if there is a possibility of a pregnancy it would be reasonable to check a pregnancy test when bleeding starts - if negative then it is the period, if positive then implantation bleeding.