Glow/ovulation tests versus the doctor. HELP.

So for the past nine months my ovulation tests have matched up with glow pretty exactly. But when k had my doctors appointment my doctor wanted me to go get blood work done on day 21 of my cycle to make sure I am still ovulating. My thing is that day 21 is definitely after the projected date glow gave me. I know the doctor is a doctor for a reason but I'm so nervous that it's missing the time frame that I'm ACTUALLY ovulating. Can anyone shed some light on this?