I'm usually so spot on with my opk's this month with one thing or another I've missed CD 16/CD17 and it looks like I've already ovulated from my CD18 opk.. I've never ever ever had a positive opk at CD18 I have no clue why I've potentially ovulated late this month. Im a regular 28 day cycle and always get a solid positive opk either CD13/14... See attached photo for this month.
I baby danced
CD 12,14,15,16,17 and now 18 
It was never this hard get pregnant with my first 2 who are now teenagers.