PROGESTERONE AT 13 WEEKS PREGNANT

At around 8 weeks, my progesterone was 18. A month later, at about 12 weeks 5 days, it was 19. I am now 13 weeks 4 days. My doctor is keeping me on my supplements. I take 60mg capsules. I've asked her to switch to the suppositories or up my dosage. But she said that the goal is to get my body to start producing it's own progesterone. which doesn't make sense to me.. because what if my body won't start on it own?? I'm worried. Is this progesterone level too low?? After receiving the results from my doctor, I had to check the baby's heartbeat with my doppler because I'm so worried about low levels being associated with miscarriage. Advice or thoughts?