progesterone level dropped--what does it mean?

My doctor just called and told me everything looks fine but my progesterone level dropped significantly in a matter of two days from 24 to 19. She says this 19 is still "normal" but is concerned because it dropped. I am 5 weeks and 4 days. She prescribed me medication to take for the next few weeks. But, I am already absolutely panicked. Why would it drop so much--what is wrong? :( Also my bloodwork was done on Friday and I just got results today, it could've dropped so much more since then. I am super worried.