Progesterone?

Caryn
Hi everyone!! 
I heard my baby's heartbeat today at 7wks 2days! It wa 138bpm and my hcg looks good. I've been taking progesterone suppositories 3x a day since we found out. My progesterone dropped from 25 to 18.6. They called to let me know it's under 20 which means we need to keep an eye on it...should I be concerned? Everything else looks good but I'm stressing about this one thing!