early blood test

My last period was roughly 30days ago, (last period started 5/1/17) I was due yesterday going by my period apps and still no sign at all. My dr gave me a pregnancy blood test roughly 7/8 days before my period was due and she said my definitely not pregnant as there was 0hcg. Has anyone else had a negative blood test test but been pregnant? I did have this with my first but thinking the dr may of not checked my bloods properly as he was a twit lol I stopped the pill 2 months ago. I meant to start taking some meds but can't be on them while pregnant so not sure what to do. They caused me too have a miscarriage last time so I'm really not wanting to take them till I know for sure but medically I need too. Tia