Test results and progesterone

I had blood work yesterday for HCG Quanitative and P4 level. Hcg was 93.3 and P4 progesterone was 15.4. The OB said my levels look good but would like for my P4 level to be above 20. So she put me on Progesterone 200mg capsules vaginally for 4 weeks to help ensure my progesterone increases. Anyone ever have this before? I’m 4weeks 4 days today. I became pregnant naturally. And never had blood work or anything for levels with my first child. So this is new.