OPK- Peak Fertility

Hi all
Hoping you can help. Peak fertility according to the apps I use is Sat-Sun this week. 
Did an OPK yesterday (Clearblue digital) and it was Low. Did one this morning and it's Peak!
Anyone else miss the high days? 
(And I'm using OPKs for the first time in a few months so if I'm ovulating earlier than the apps, would be why nothing has happened yet.)