I had some of what you're talking about. I had my three older children and then had two children die and then had our youngest. My children who passed away were 16weeks and 31 weeks. To be honest, we had decided to not have any more and that I was going to become as healthy as I could. I figured that it was normal for a woman to be able to carry a child to full term and not normal to not be able to. Therefore their must be something unhealthy about me. I went back to my OB that uses Naprotechnology, as form of tracking a woman's cycle or hormonal changes. They found that I had an infection that went totally undetected, my progesterone was low, and that I had a thyroid issue that also was overlooked. In the end I found myself pregnant with my youngest. She is the best surprise gift I have ever received. I had to supplement my progesterone and my T3. I went back to my old OB and asked him to work with my OB that uses Naprotechnology or at the very least respect his medical processes because I needed someone local to deliver the baby. I am so thankful everyone agreed to work together because had I not had the Napro. Doctor's practice I would have lost this baby also.
I don't know of any diet that would increase your progesterone. Mine was so low that I had to take injections twice a week for nearly the entire pregnancy. Most doctors will only test for progesterone in the first trimester and not after that. Had I followed normal procedure, my daughter would not have made it. I could feel my progesterone begin to drop and I would begin to go into labor.
I would recommend finding a doctor that is trained in Naprotechnology. I was fortunate enough that the Doctor who created the technique is only an hour and a half away. After a couple of visits, most observations and blood work can be done using any local lab and sending the information in through emails.
You can look up the web page. Dr Hilgers is the doctor at the Pope Paul the VI Institute. He has been training doctors for years from all over the world.