Never had a positive OPK!

I'm so frustrated, I'm on my second full month of doing opks and I still haven't had a positive or even anything other than a really faint second line. My cycles are really long, 35-40 days and I've been in my so called fertile window for a couple of weeks now (glow just keeps moving it back with every negative OPK). 
Last month I got some bleeding half way through which made me think It was AF and I had missed ovulation which meant I spotted doing opks then glow assumed i ovulated in that gap but I'm not convinced. 
I'm waiting until AF comes this month before going to the doctor with the results to see what they say- has anyone else had long cycles and periods but not actually ovulated? I just want a fertile day!!  Do you think there's a chance I am missing the spike? I would at least expect a second line to appear when I was close though?
(Ps- it's 2 years since I came off the pill for BC and I'm also tracking BBT and taking OPKs every afternoon).