Ovulation

I'm so confused. According to Glow I have a 33% chance of pregnancy tomorrow so I've been taking opk's daily since Saturday (13th) because I'm following the SMEP method where you start taking daily opks on cycle day 10 until you get a positive but every single test has been negative. I have ewcm which is what prompts me to do the opk but I get nothing? Not even faint lines? I thought opks were meant to get darker and darker leading up to ovulation? Could this mean I'm going to ovulate later even though I'm experiencing fertile cm right now?