Yes, Duffy, Prometrium is the most natural form or progesterone but it isn't as stable or effective as the synthetic progesterones - especially when used orally. However, there are supposed to be fewer cancer risks with micronised progesterone - though the risks before 60 for any HRT is very, very small.
We can't win really.
I eat small(highly nutritious) amounts often(so every 3-4 hours) and do lots of brisk walking - I've managed to get my weight stable doing this. DG x