Positive opk but negative blood test

Hi ladies. I have had two strong positive opks the last two months, went for my day 24 (later due to long cycles) progesterone check and both months have been negative for ovulation. This last one was only 3.6 at 4/5 days past positive opk. This has really confused me and I was just wondering if anyone else had been through this or could offer any insight/advice. Tia xXx