Cd 28 positive opk

I am so confused and upset. This is my second cycle on letrozole. First cycle confirmed ovulation cd 16 with doctor. This cycle I was hoping for same results, I got what I thought was peak opk on cd 15. Bd all freaking week! Thought we had a solid chance. But at the same time had zero cm so I was thinking maybe I really wasn’t ovulating. Fast forward to cd 28, I am now getting tons of cm and blazing positive on opk! Has anyone ovulated this late on letrozole? Does that mean it didn’t work this cycle? Should I call my doctor and tell her? Maybe I need a higher dose? Why did it work perfectly the first cycle and now I’m back to opk confusion? Any insight would be greatly appreciated?