With progesterone it really makes a difference where you get your levels checked. With my last pregnancy I had to have progesterone shots all the way through the pregnancy. They say that after the first trimester your uterus will produce the progesterone and quite testing. Had I followed regular protocol, my daughter would not have made it. I also had the same blood tested at two different labs with a 30 point difference. Apparently the kid of progesterone was also important. I had to take shots for the entire pregnancy and towards the end I also had to add progesterone in pill form.
Also check into thyroid. Make sure they look at the ratio of T3 to T4. My levels individually came in at normal rates, but the ratio was off and I ended up supplementing T3 for half the pregnancy.
I also had them check to see if my uterus was misshaped. I can't recall the term for it. Depending on where the baby attached to the uterus, the pregnancy would survive.
Find an endocrinologist or find a Doctor trained my Dr. Hilgers of the Pope Paul the VI Institute.