I Am Always Regular With My Menstrual Cycles. My LMP

I am always regular with my menstrual cycles. My LMP was 11/10/2014. It is now 12/22/2014 and still no period. I have never missed one in my life. I had intercourse during my "fertile window" and have symptoms and so much white/clear discharge, but 2 negative pregnancy tests. My diet or stress levels have not change, so what could be anothercause? I want to go in for an ultrasound but I'm scared to find out that I'm not.