Pregnancy test

Hello, I have some concerns about my period and my wishes of becoming pregnant. In September 2018 i had a miscarriage I was 6 weeks, after that I had my period normal but the cycles were from 28 days to 33 days. In December I had the longest cycle which was 38 days but now I’m 11 days late with a negative pregnancy test, the doctor prescribed me pills to regulate my period and get pregnant easily but I’m skeptical about it. Should I go and ask them to do a blood test before I start the birth control? Or should I wait another week to do another pregnancy test. I really want to get pregnant but I feel me thinking too much about has something to do with this. Help please!