I am curious to ask... what happens to progesterone levels from the day of Ovulation to CD21??

And I'm asking because I have had a couple of CD21 blood tests and my levels were in the 30's, but this cycle I had a bt to confirm ovulation and it was quite different in results.

So what happens (or is supposed to happen) in those 7 days?
Do the levels rise, fall, stay the same??

Does anyone happen to know?

TIA, Sonya.