So I sent Ysa a message but though i would post it here too... I googled progesterone and found this...
Because progesterone is essential to prevent the premature shedding of the supportive secretory endometrium, a significant drop in progesterone levels or blockade of progesterone receptor sites during the first 10 - 12 weeks of pregnancy may result in the loss of the embryo (miscarriage).
Women with a history of miscarriage should begin using progesterone cream as soon as they know they have ovulated, to supplement their own progesterone and offset any environmental estrogen effects. (Using progesterone before ovulation can create a hormonal signal that tells the brain not to ovulate)
If you want to be pregnant and you're using progesterone cream, it's very important to keep using progesterone cream until you find out whether you're pregnant. (You can take a pregnancy test a few days after your period would normally be due.) The sudden drop in progesterone levels created if you stop using the cream can cause what is, in effect, an abortion, by bringing on menstruation.
If you find out that you are not pregnant, stop taking the progesterone on day 28 of your cycle or whenever the last day of your cycle normally occurs. If you are pregnant, keep using the progesterone every day in normal doses. It's fine to use it throughout your pregnancy, and it's important not to stop it suddenly until your third trimester when the placenta is making so much that it won't notice if there's a drop of 15 to 30 mg a day.