There could be a ton of reasons why...maybe you didn't O when you thought you did? Maybe your body geared up to O, and didn't? Sometimes it makes absolutely NO sense why it didn't happen...I hate that! I wish I could tell you just by looking at your chart, and at the same time, I wish all you had to do was line up Oing and BDing and BOOM--you're pregnant, but it doesn't always work that way, and it stinks!
Good luck to you hon...and just remember, it's never over til the witch shows!