This month I've been using the Clearblue digital opk kit with the pink sticks, which show a blank circle for no surge or a solid smiley face when it detects the LH surge. Problem is I've been getting negatives. I was a bit hesitant to use fmu as when I've used OPKs before I've always tested in the afternoon. I've followed the instructions and used fmu and have been testing once a day since CD15. I've tended to get a positive around CD 18.... Tomorrow morning will be CD 21 and my CM is creamy now. I'm annoyed that I may have missed it??! Has anyone else had a similar experience? I'm not sure how reliable these tests are.