Miscarriage

I recently had a miscarriage on May 17 of this year. I was 12 weeks pregnant. Two weeks after that I had my period that lasted two weeks. I am now finding it very difficult when I will be fertile. According to this app I should of started my period last Friday and I still have not started. I took a pregnancy test this morning and was negative. Anyone have any ideas when I should be starting my period or be fertile.