How many dpo should I start progesterone?

Backstory, I’m on 50mg of clomid CD 3-7. I had an ectopic in January 2018 (methotrexate, no tubes lost) and I just had a chemical the beginning of this month. My progesterone was only 2.1 or somewhere around there.

My OB put me on progesterone pills 400mg two times a day, but he told me to start them the day after a positive opk. I used strips and the clear blue advanced and got a solid smiley Tues July 17th, and got dark lines on the strips as well. I also had some very obvious ovulation pain/discomfort on the 17th. Since I don’t temp I’m being safe and assuming I ovulated Wednesday the 18th. I’ve read how you should wait until 2-3dpo before starting the progesterone. I took my first progesterone pill this morning, but now I’m nervous I’m taking it too early? I believe I’m at least 2dpo today, but I could also be 3dpo if I go based off of the pain/discomfort I had Tuesday.

Does anyone have any insight?