13.9 Progesterone level at 8w4d appt

Hi mommas! FTM here and had my 1st prenatal visit on 7/17 where they did blood work. Just received call that my progesterone level was 13.9, but they like to see it closer to 20, so will be prescribing me supplement. Has this happened to anyone before? This is all new to me, so not sure if these low levels are why I haven’t had much symptoms besides fatigue and sore breasts. Baby was measuring 9wks and heartbeat of 176 at same visit. Thanks! Trying not to worry myself out