Irregular periods

Whitney
I've been tracking my periods since June and My cycles switch every other month to a t. As follows: June 28 day cycle, July 36 day cycle, August 28 day cycle, September 36 day cycle, October 28 day cycle, November 36 day cycle, December 28 day cycle and just now was a 36 day cycle even though a ultrasound showed I would ovulate on the 19th day of this last cycle.  Can this affect fertility or does this mean I'm not ovulating? I'm so confused?