Hi Nattie! I think CD18 sounds good if that was your only patch of CM. I don't rely on post O symptoms, like sore bits, breakouts and the like, they can easily change (mine sure do! Apart from a massive slow down of my bowls, I unfortunately get that my whole TWW every time). As for hopefully being a pregnancy symptom, when did the sore nipples start this time?
AFM, surprisingly got my crosshairs, so it appears FF agrees with me on O day. Was expecting to have to argue with it!