When do I start OPKS

Shanteria
I start OPKS after my AF is off correct ? We've been TTC for 4 months so now we're trying the OPKS. My AF is due 08/29 & glow says it ends 0n 9/1. My AF is pretty regular it's just super light. My boobs are super sore & been sore for about a week now, took a test & got a BFN! & for my CM I don't really get egg whites or such I barely get anything, is this gonna make it harder for me to get pregnant or I just have to figured out my fertile peak!