The mini-pill is progesterone only and is abortafcient i.e. one of the ways it works is to prevent implantation. You can search it up on the net. It contains synthetic progesterone and no estrogen. It's the combined oral contraceptive that contains both estrogen and progesterone.

The doctor tells me that the 10 day course of progesterone pills she wants me to have don't prevent pregnancy, but I am highly dubious because

1: She does not consider pregnancy to start until implantation, where as I believe it starts at conception (even though there is no actual pregnancy until implantation, there is a life from conception)

2. If the pills force the lining of the womb out, it could prevent implantation.

I don't know about natural progesterone and how it differs from synthetic. But definitely the mini-pill is progesterone only.