Hi, My girlfriend and I had unprotected sex a little over three weeks ago.  She is supposed to get her period this last week and hasnt.  She hasnt used her birth control for about a month because she was on antibiotics and was told it wouldnt help anyway.  She tool plan b within 24 hours of the incident.  Is it normal that she still hasnt had her period?  Please, any answere are appreciatie!!!!!! Thank you!