Am I not ovulating? Please help!

Emma

Hi, I thought with the dip in temp that I ovulated cd15 but then got a positive opk on cd 21. Still no sign of AF so I guess I didn’t ovulate on cd21 either? Last month I had a 38 day cycle and a positive opk on cd 15 but that means I didn’t ovulate cd 15 or AF would have come earlier than cd 38? Finding it hard to know when I’m ovulating as CM, opks and temps aren’t all matching.