Hmmm, I would normally go by EWCM, but sometimes I get that throughout my month and I have "O"ed.

If you are unlucky this month which I hope you are not. I would start using your OPK's from CD12 that way you could see when you are o'ing. You could be getting your "o" date wrong.

Another way to check for "o" is your cervix pos. Its normally High, Soft and Open for conception!!