A couple of questions about recurrent miscarriage

[Cricket]

Hi ladies. I'm not sure if this is exactly the right place to post, but I'm hoping you might have some info to help me out here.
DH and I have 7 beautiful children, and up until this year I had never had a miscarriage, though it did take us over a year to conceive some of our babies. Over the past 5 years, I have been trying to get my weight into a healthy range. I was 215lb (97.5kg) and have gradually worked down to 142lb (64.5kg). I am 5'7" (170cm) and my weight has been stable for a little more than a year. I exercise (pilates/barre/light weights/cardio) 30 min, 5 X week. Over all, I feel healthy, energetic, and happy. My cycles vary 2-4 days per month, but are generally regular and predictable.
We began trying for another baby in January of this past year, and conceived immediately (when it used to take a few months at least) but I never "felt" pregnant, and miscarried at 7 weeks. We were advised to wait a month before trying again, but we had a little slip up and conceived again right away. (again - this was unusual for us) This time I felt pregnant - nausea, fatigue, etc. Miscarried again at 10 weeks. We decided to wait a couple of months. Tried again in August. Conceived right away, had some early symptoms, pregnancy tests had stronger and darker lines as the days progressed, but I miscarried a week later.
My family doctor has referred me to an ObGyn because she thinks I might need to take progesterone. She also suggested that I might need to gain a few pounds. I've done a little reading about progesterone, and I don't feel like I have any of the symptoms of low progesterone. It also seems to be a little bit controversial as to whether it's effective or not. And I find it a little hard to believe that my weight (which is right in the middle of the healthy BMI range) could be an issue. But I am willing to give these things a try if they are likely to make a difference.
Can anyone give me any other insight or suggestions or share their experience? Do you know of anything else I should be asking about? Chromosomal issues are unlikely, since we have healthy children already. My bloodwork and thyroid levels are normal. No sign of lupus. I'm 34, so getting a little older, but I don't think I'm in the "too old to conceive" category yet.
I'd appreciate any help or info you can give. Thanks!