Shellie, I wish I had some advice for you. For me, some months it is easy to detect. I have a temp dip the day I O, and a temp spike the day after O. But other months (like this month for me...I have a very gradual temp rise. I'm sure that doesn't help, but wanted to let you know that you are not alone in your confusion. Take a look at my chart and you will see what I mean. FF says I O'd on CD 14 but I'm convinced I O'd on CD15 because of all the other signs...CM, CP, and a amazing increase in sex drive!
FWIW though, by looking at your chart, I would say that you definitely O'd on CD 13! But the trick to an O+12 is to figure out when you CM has shifted. When did your notice you CM shift? Was it the next morning on CD 14?