Progesterone

Just found out I'm pregnant after another miscarriage.. I'm 5 weeks today and the doctor ordered hcg without progesterone. She called to say hcg level is around 2150 and because of my history, to repeat in two days and start taking the progesterone she called in to the pharmacy. I guess I just find it weird that she didn't check my progesterone level and just went ahead and prescribed it.. Anyone have experience using this stuff?