I had sex on the 18/20th of November and we used a condom and I know it didn't break. I checked my ovulation calculator and it said I stop ovulating on the 17th. I haven't gotten my period but I have been cramping. I just wanted to know is there such thing as an invisible period? My aunt thinks I am pregnant but I know it can't be that. My last period started on November 1st. My menstrual cycles never flowed correctly before I started having sex on the 18th.