I had sex 3 times 2 days before my period. i am on diane-35, only contraception used. i took my third period pill and still don't have it. could i be?

Menstrual cycle: If you have an irregular menstrual cycle it is difficult to tell when you will ovulate though on a regular cycle ovulation occurs approx 14 days prior to starting your period so it is unlikely that your egg was viable at that time there is always the possibility. If you have take a Plan B type of contraception in the correct time frame that will decrease your chances as well.