I'm still having some trouble with these things. I've been TTC for three months now since I lost my baby at 21 weeks.
Last month I tried the clearblue OPK and never got a smiley face. This time I tried the cheap sticks from ebay and two days ago it went from an amlost invisible second line to just slighty weaker than the test line. I thought that might mean my surge was very close but after two days of the same result it's gone back to barely there again. I dragged my husband to the bedroom for those days anyway just in case that was my surge so keeping my fingers crossed.
Has anyone else had this result where it never gets as dark or darker than the test line but does alter a bit for a couple of days?