20MM FOLLICLE BUT NEGATIVE OPK? Help

Hi guys, so I had a follicle scan yesterday and i have a 20mm size follicle. My dr said she expects me to ovulate this weekend. But my opk clearblue advanced doesnt show the (blinking) smiley. I was on 50mg clomid (3-7) am on cd12 today. What day did you ovulate with clomid? Anyone experienced the same? Help :(