So last month on July 13th I had sex with my boyfriend and it was a mistake. It was 4 days before my period was supposed to start and he didn't use a condom and I was not aware of that until after when he freaked out. 12 hours later he bought me plan b and I took it. I was 3 days late on getting my period and it was lighter than normal. I am now 15 days late for my expected period. I took two pregnancy tests last week and both were negative and about a week or two prior to that I had taken one as well which was also negative. Could I be pregnant or could the plan b have changed my cycle? Could I be late because of stress? My cycle has been irregular for the majority of the time I have had it and I have missed months before but for the past 6 or so months its been daily normal.