The times that I've gotten the darkest lines has always been around cd9 or cd10 which coincided with ewcm. Problem is this past couple of months I've been on antibiotics and I have no cm to go by, so now that I need them most opk's are failing me. I'm afraid it may be my hormones because my last AF came on cd17 which is not normal. It usually comes on cd24 to cd27. I've also been temping for these past two months, but I'm still new at this. FF had me OV-ing last cycle at cd9 but opk's would not confirm. Baby Med experts could not detect OV, so I don't even know if I am OV-ing. Soooo frustrating!!