Anyone ever taken Letrozole?

I've taken the letrozole the last couple of months (2.5mg, my doctor won't up the dose without doing mid cycle ultrasounds and testing @ 2.5) and this cycle I got two days of positive OPKs and now I'm about 2 weeks late for af with all bfns. Is it safe to say I didn't ovulate? I'm thinking I might have to take provera to get a period again 😞 any input or experiences would be appreciated!