Why am I not pregnant?

I had a miscarriage at the beginning of August with a chemical and ovulated that month and this month. I am due for a period of Tuesday but have been getting BFN's. I don't understand why. We had sex everyday during my fertile window. I know I ovulated for sure both months and I had some cramping that I thought was the baby trying to implant about 4 days ago. I'm frustrated. I guess I don't get it. I just want to cry. How can I have ovulated and not got pregnant when sperm was present?