Help! Dropping progesterone

April

My progesterone was drawn at 4 weeks and was 23. I've been on 600 mg progesterone daily since 3 dpo. My progesterone was rechecked at 6 weeks and dropped down to 15. Has anyone had such a big drop and still had a successful pregnancy?? I'm kind of freaking out since I've had 3 early miscarriages before.

To add, my HCG went from 850 at 4weeks to 1771 at 4+2 weeks. Haven't had it checked again since.