Falling progesterone levels

Had a great 7 week appt on Thursday! Measured correctly, 138bpm heart rate. Got my blood tests back today and everything came back normally except my progesterone (at 4.5 weeks it was at 16 but now only 11). Starting suppositories tonight. Is anyone else dealing with this? The doctor didn't really give me any details so I'm not sure how common this is or what it might mean since everything else looked good.