I had unprotected sex on Jan. 7th and 8th. I got my period after, on the 8th. However, due to unfortunate circumstance I took plan B on the 8th as well. About 21 hours after having sex. I was ovulating on the 15th. Than had unprotected sex again. I am on a 21 day cycle. Which means I should have got my period on Jan. 29th. I took a pregnancy test on the 30th. It was Negative. I have been told that the chances of me having a child are very very slim. My cervix is slightly swelled. I have symptoms of my period coming. I also have no symptoms for pregnancy. Minus being emotional and pressure in my lady area when I cough or sneeze. What are the chances that it could have been a false negative?