L., my heart goes out to you and your husband. I have PCOS, too, and have been misdiagnosed, undergone unnecessary surgeries, and had several miscarriages. Who is your doctor? Besides Metformin, what is the long-term plan?
Personally, I was taking Metformin and it helped reduce inflammation and get my periods more regular. Be prepared for the side effects, which include cramping and having to go to the bathroom FAST. You get used to it. BE SURE to eat before you take it. EVERY time. I could never get up to the 2000 mg they wanted me to take, instead, I could only take 1500 mg. So, listen to your body and know your limits.
I'm not sure if this prevents miscarriages, as much as it regulates your PCOS. In fact, I am not sure that PCOS is the reason for miscarriage.
With this many miscarriages, you may want to consider also having genetic testing done to see if you or your husband have a chromosomal abnormality. It's a simple blood test. The cost is $400 -- which includes both you and your husband -- and it takes a couple of weeks to get results. A fantastic doctor to see for RPL (recurring pregnancy loss) is Dr. Carolyn Coulam. Her office is in Evanston. Very much worth the trip. http://www.illinoisivf.com/physicians.htm
Best of luck to you, L.. If you want to talk more, I'm happy to share my experience.
I hope this helps!