Go by your OPK. If you notice fertile CM later on in your cycle, consider yourself fertile and BD, but I would also BD today and tomorrow, possibly Tuesday because of your OPK result today... HTH! Also, if you are lacking in fertile CM (I was because of recent BCP use), you can try preseed (love it) and/or evening primrose oil. I take 2000 mg up until ovulation, then I stop.