OPK question

Heather
I have come to severely distrust these things.
Yesterday I took a Wondfo, a Clearblue Advanced and a Clearblue Easy.
Wondfo was negative.
Clearblue Easy was low fertility.
Clearblue Advanced was low fertility.
This morning I took a Wondfo, a Clearblue Advanced and a Clearblue Easy.
Wondfo was negative.
Clearblue Easy was low fertility.
Clearblue Advanced was peak fertility.
Why?!?!