OPK's... What a minefield

Been using opk's for the fist time this month and been tracking since my period just to get to grips with it. Lines have been steadily getting darker. By no means positive dark then today nothing not a thing apart from the controll line. Tried two different brands as well. I am suppose to be within my fertile window today too...?? I've also been tracking my CM and CP and don't think I've missed ovulation! Any thoughts?