MC while on Progesterone supplements?

I've had two early miscarriages and now pregnant again. My doctor, although not believing they make a difference, agreed to prescribe progesterone suppositories (twice daily). Just started week 6 and started the suppositories yesterday. I researched and find a lot of women writing about their experience with it and that after taking the suppositories had successful full term pregnancies. Very encouraging! I am wondering though, if there are any women who still MCd even with the Progesterone treatment and if so, what was the dosage your doctor prescribed?