In the heat of the moment I had unprotected sex with my boyfriend and he did NOT cum inside me. I took plan B about an hour after. This was friday the 15th and I should have started my period the next day. It is the 17th and I am having intense cramps but I haven't started my period yet. Is this normal? Is there there an average amount of time that plan B delays periods? At what point should I begin to worry if I don't get my period?