OPK Question

I’ve never used opk’s before and today was my first time using them. I’m on cycle day 14 and felt like I was ovulating yesterday into today .. but I took two opk’s and the line was so faint I could barely see it. The app says I’m supposed to ovulate in 2 days. So my question is— can you have a vfl and then really dark line the next day? I feel like the line should be darker now if I’m ovulating soon and I’m in my fertile window starting today. I’m so confused! HELP