Progesterone Level LOW?

Megan

My doctor just called with my lab results. My HCG was 40, which my doctor says is normal. My progesterone on the other hand was 16.1, he acted like that was low. The doctor now has me on Prometrium 200 mg twice a day. I was only 3 weeks and 4 days pregnant when the lab test was performed. Anyone else have any issue with their progesterone? Is my low? Anyone have a successful pregnancy after?