I won't be much help, I just wanted to say I am experiencing something similar. I had a 26 day cycle, and a 33 day cycle so far this year and I'm on cd19 and I've not o'd yet this month. I've not been tracking anything other than for tta until a few weeks ago. I'm pretty sure I've been o'ing up until this cycle because I've had EWCM around cd14/15 every other month. I think I might need to start temping since my DS is finally sleeping all night. Anyway, I just wanted to offer my sympathy. I hope you figure out what's going on!
My iDevices are out to get me. Please excuse mistakes.
Elisha, wife to my amazing husband and SAHM to my beautiful baby boy, Titus.
Expecting our new little one December 2013!