Clear blue digital OPK helpppp!


Quick ovulation question... so I am currently on cycle day 12, I started testing on cycle day 9 which was low, cycle day 10-12 have been high, so I decided to test again tonight & it was low again? Has anyone ever had this happen? I am using Clear Blue digital OPK, & this is also my second month taking Femara 5mg on cycle day 3-7. Can anyone help??

-Last month I took Femara 2.5mg cycle day 3-7 & had my peak on cycle day 12 at 10 PM.