low progesterone. starting medication tonight.

I had a miscarriage back in June of this year. I was about 6 weeks.
I am 5.5 today(with it being Monday).
I went in this past Friday to have my blood drawn to check my levels to ensure they are not the reason I may have miscarried last time and potentially could miscarry this time. (I was 5.2 weeks)
My Dr called me this morning and said my HCG was in a good range. But that my progesterone was at 9. She stated she wanted me to start a medication to help with my progesterone.
Has anyone had any experience or success stories with this? I am just worried that my progesterone will drop or that the medication will not help. Or that 5.5 weeks is too late and that I should have started it earlier since I miscarried at 6 weeks earlier this year.