I have a question.

I had a baby 4 months ago (our baby boy passed away 14 days after he was born), two days later I got the Depo shot for my birth control, I had my period the whole time (literally, constant light blood, stopped every so often). Well, I went back for my 6 week check-up (really 2 months) in October and my midwife said to start Tri-Sprintec (oral birth control) on November 16th. Well, I started my period October 13th, lasted until the 17th. November came, I expected to start on my birthday, it never happened. I started my birth control 3 days later. December now, still no period. I took a pregnancy test and it was negative.. I'm not sure of what I should do..