Please help Opk confusion

OK I have had 3 days of positive opk strips with I believe the darkest test line last night but there is so little difference it's extremely hard to tell all are nearly as dark if not matching the control...I've had mild cramps all week but extremely bad cramps today on the right side to middle...has anyone ever had this or know anything? We have bd all week so I know I'm covered there and it was painful night before last but I thought I Od earlier in the week...sooooo frustrated!!