What Causes Delayed Period And Yellowish Vaginal Discharge While HPT Is Negative?

I'm 12 days late. I took several pregnancy tests that say I'm negative. I also have nipple tenderness and sore breast that are itchy. Accompanied by really mild cramps that come and go. Light pain in my lower back. I'm also experiencing a yellowish discharge. I'm very exhausted all the time too. I'm very regular and I always get my period on the 28th or 29th day. So this is very odd. My last period started on dec4 2014 and haven't gotten it yet.