How long is your cycle normally? If it stays pretty consistant, you can subtract 12-14 days from when you expect af to arrive and that should be around when o is. If you are more than 3 days past that window, it is unlikely that you would still be fertile. But, if still in that range, I would keep it up.
Thank you for your reply, no i havent tried them yet but thinking of starting next month if nothing has happened do u think i should carry on bd every other day from now on incase i might ovulate later??
Cm is a pretty good sign of o, but by itself is only about 30% reliable. If it was a correct indication, it could be that same day up to several days later. The time frame for o was pretty good at cd16, so you just may have caught it. Ever try opks to cross check your fertility signs? Good luck and happy tww! :)