12 weeks pp and still no period!

Hello ladies,

I had my son on 6-21-17 and he will be 12 weeks tomorrow and I'm not breastfeeding, and I still haven't gotten my period!!! Like at all! I bleed till about week 5 after he was born but nothing heavy and I was expecting my period after that! My doctor told me it would be about 6-8 weeks after my son was born and then I'll have my period! Well 6-8 weeks have come and gone! What should I do!! I've taken multiple pregnancy test all negative! No even slight positives at all! My husband and I have been safe but I'm not on birth control! ( I got some birth control at my 6 week check up and he told me to start it the Sunday after my period!) help me ladies is this normal! What should I do!!