My period was last on the 21st of August and it's now the 21st of October. I had intercourse on the 18th of September I believe; using a condom and he didn't ejaculate (it was my first time). My periods are usually around a month apart. Since then on October the 13th I had a pregnancy test with Brook a sexual advise and help oganisation and it came back negative, but I still look on the internet every day for all the symptoms. Why haven't I had my period?