Hi Mandas,
So sorry to hear of your losses. I am not a medical doctor, but have 6 yrs of infertility (including 5 pregnancy losses) behind me and can advise on the basis of what I have learned over that time!
As far as I know there are basically 3 ways that progesterone is used after recurrent pregnancy loss / for fertility issues.
The first is the use of a progesterone pill (like the contraceptive pill) that is used prior to a cycle of fertility treatment to 'regulate' or control the cycle (basically it is a convenience thing so the clinic can be sure it is open on the days you need scanning etc.).
Secondly, some pregnancies are lost because there is insufficient progesterone to maintain them for the first 10-12 weeks until the placenta takes over. This sometimes leads to early losses and what is called 'luteal phase defect' - when there aren't enough days between ovulation and the womb lining being lost as a period - the fertilized egg has no time to implant / may not be able to implant because conditions aren't quite right.
In this second case, the preferred treatment is usually pessaries (or suppositaries - less messy!) of progesterone in a waxy substance. These 'botty bombs' (as we used to call them - they do look like missiles!) are called Cyclogest, and are the first line of treatment for some docs- usually you will be told to use the from ovulation till a period - or till 10-12 weeks if you do get pg.
The third treatment is Gestone injections - these are intramuscular injections of progesterone - usually in the bottom - and can be a bit sore. These are sometimes used in addition to or as an alternative to Cyclogest if low progesterone has been identified as an issue.
As an aside, lots of ladies who have suffered recurrent miscarriages have had success with baby aspirin (75mg per day). You can pick it up over the counter. I took it with my folic acid and up until week 30.
Hope that helps. And good luck.