No opk test line at all?

I've been doing opks for 10 months roughly. I have always gotten a + lh surge around cd 13. I'm on cd 12 now and there isn't a second line at all. The past 2 days also stark white. I even tried different tests and there isn't anything there. Usually by now the test line is nearly as dark as the control. I thought that there is always lh in your system so there should always be at least a faint test line. I don't have pcos so idk what to think. Has this happened to anyone else?