Hi, I am 25, Single Female. I had unprotected sex on 19th July 2010(Jst 2 days after my periods cleaned up), but did take a contraceptive pill within 24hrs. My period was due on 21st this month, but missed, I took a home pregnancy test, it was negative. I also went to the hospital and got the UPT done, that also is negative. BUt I still havent gotten my periods. What could possibly be the cause? Do you recommend any tests?