Letrozole Help!

Ok I need help from you ladies.. so I was on letrozole to make me ovulate bc of my PCOS. I went on a Monday 4/16 to get a ultrasound and was told I had a 17mm follicle and should make sure to start having sex at least every other day for a week or so. we've obviously done that plus some but .. any idea on when I would/did actually ovulate or when I should test?? I've been disappointed with so many negatives I don't want to test too early and start losing hope again. help!