I had my periods between the 23rd to 27th november, i had sex on the night of 8th december but he did not ejaculate inside me, i took postinor 2 tablets the two at once the following day guess after 15 hours, my periods were supposed to come on the 18th or 19th december but they have delayed. i took a pregnancy test and it is negative, i have abdominal pains, Why have my periods delayed? could it be that am pregnant?