Question about opk

Shayla
Hello I am very confused I started using the clearblue adv digital ovulation test and it always comes up as low fertility. How many days after your period is your peak or high usually? My period lasts about 5-6 days and is pretty regular. I was wondering how accurate they are bc my <a href="https://play.google.com/store/apps/details?id=com.glow.android">Glow app</a> shows the complete opposite. It shows that I should be at my peak today with 28% chance of conceiving yet my clear blue says low fertility. Please someone help. I'm new to all this and TTC #1.  Thank you so much in advance.