Have you tried taking B6 to lengthen your LP? Not trying to worry you, but your issue could be your luteal phase and not a variation in what day you ovulated. I take 100mg pre-O and 50mg post-O. I went from having approx 10 day LP in January to something like 16 days last cycle (although I am not 100% because I don't know the exact day I ovulated) and taking B6 is supposed to be helpful for your fertility anyway.
Just wanted to suggest it to you and HTH!!
GL and FX!!