Late period

Ok so my last period was 12-12-15 I've always had a very regular 28 day cycle... as of today I'm 20 days late for my period and I've taken several tests which were all negative and even had a blood test done when I was 6 days late which was negative. I have a appointment scheduled with my obgyn for Wednesday and I'm hoping to get some answers. Has anyone else experienced this and what was the outcome?