What Causes Delay In Menstruation Other Than Pregnancy?

I finished my period on September 29. Two days later on October 2 I had unprotected sex with my boyfriend. On October 3, I took Plan B one step, which was 13 hours later. I had some light brown discharge, not a lot of it six days after I took the pill. I was expecting my period October 24 and did not get it, so I took a pregnancy test the 27th and then the 30th, both came out negative. I still haven't gotten my period and have white discharge that is stickier then usual. Am I pregnant?