Letrozole and OPK

A

This is my first cycle on Letrozole and I have been testing ovulation with an OPK but I have gotten a negative every time. Before I started taking Letrozole I would get a negative for 1-2 days after aunt flow, then high for 10ish days, but I would never get to peak. Has anyone had similar problems and still ovulated? I have a feeling the dosage of Letrozole is too low.