almost 3 weeks late! No positives.

I'm 19 days late for my period, loads of tests later and they all are negative. My last period only lasted a day which isn't normal for me, but my last normal period would of been before Christmas. I have a few different symptoms. I went to the doctors and they just said wait a few weeks and re test. But I just wonder what's going on with me. Advice please or has anyone gone through this and realised they were indeed pregnant?