Progesterone levels

I went in for my 10w5d ultrasound and pap today. Ultrasound was great, baby was very active and heart rate was 168. My nurse went over my blood work from last Thursday. Everything looked good, but I am anemic and my progesterone was at 20. When I was taking Endometrin at 4w it was 25. I stopped taking it last week Wednesday. Nurse said numbers were good, which I know they like it to be 20 or above but, should it have dropped this early? I know they will level out, I'm just a little worried due to my history of loss. Anybody experience this? I'm going to get labs done again tomorrow.