Having bloodwork done on cycle day 21 only makes sense if you actually ovulate on day 14 which it seems like almost no one does even though that's what "they" say is the norm.
My lady doctor told me to come in on CD21 so they could check my levels even though I told them I had not yet ovulated by that point and shouldn't I really be coming in 7DPO? But they said "no, no, we need to draw blood" so I rearranged my work day, rescheduled meetings, and worked from home that day so I could drive 45 mins north to get my blood drawn for no reason.
The nurse (who I actually love, it's the OB/GYN I don't like) called me this morning to let me know that my progesterone levels are low and it looks like I didn't ovulate. Yeah, no shit Sherlock - I could have told you that. Oh wait! I did!
So now I have to go back for more BW 7 days after I actually O since that was a waste of time. Meh.