Help Opk and fertility medication

Cristi

I just started taking letrozole this month. It is also my first month to take opk. I was told to start taking opk 5 days before my fertile window because my cycle is irregular. But I'm still taking the letrozole because the 5 days before fell in the middle of my dose. Opk said my peak was yesterday. Could this be a false positive because of the medication?