I take aspirin and thank God it works for the heartbeat of my baby.

I have 2 times miscarriage but this time I make sure it will never happened again, every 6 weeks of my pregnancy theres always no heartbeat of my baby in my tummy. My 3rd pregnancy my doctor gave me medicines for the safety of my baby, aspirin and duphaston and it works for the heartbeat of my baby. I don't know why my OB gave it to me but It works for me. Why she gave it to me and I don't know why it happens to me no heartbeat of my baby.