I had started having sex in December and I skipped December's period. Then when my period started again in January it was regular until this month I have started on the 17th for 4 months now and today is the 19th and I still have not started. My boyfriend and I have had unproteced sex every month, because he says he can't have kids, before and I was never late. Since I had sex the day before and the day that I was supposed to start my period could that have delayed it. Thanks