I wouldn't be suprised if your Oing but not where you normally would in a cycle either, my Dr seemed to think that was a real possibility when I fell with DD2 as they sent me for dating scans. Maybe just do it ever 2nd day JIC all the time
I was told this when working out dates with DD2. At my 12wk scan my cycle dates and the scan dates had a 9 day difference. The Cycle date was from an average 28day cycle. I do remember though we were DTD every 2nd day for a set time (day 10-16) in my cycle and then on (I think) cycle day 20 I got strong O type pains so jumped DH again JIC and low and behold I got my BFP which did not show up until cycle day 33.

All that to say, yeah I was told I O'd late in my cycle.

Goodluck OP. I hope to hear an announcement from you soon