Anyone been through this?

So my last period was in August. I have never had this happen to me as I get my period every month. I have taken 3 pregnancy tests all negative. The last pregnancy test was Oct 5th at the doctors office (urine test). The doctor knows I'm trying to conceive and didn't really see worried that I hadn't gotten my period. Instead he prescribed medroxyprogesterone to take if I hadn't gotten my period by Nov 1st so i can get my period. My question is has anyone ever had neg pregnancy tests but later found out they were pregnant? I'm planning on taking another test if AF doesn't show after the 10 days of taking the medicine.