Please help

martha
My baby boy was born in April..via csection I had a normal period last month and now I'm 8 days late. 
My periods are pretty straight forward I did breastfeed but when I quit I got my period back and now it's late..
Hubby and I have a couple times started in the moment but was quickly reminded to put on a condom.. 
Iam not on birth control because I'm on blood thinners from getting a pulmonary embolism(blood clots in the lungs) shortly after having my baby...
Took a test two days ago and it said negative
I have been alil stressed but that's never affected my periods before!! 
Is it normal for periods to be crazy after having a baby?