I'm 28, and experiencing the exact same thing, with concern. I quit the pill about 6 months ago. Two months ago, I had a 37 day cycle, then a 28, now a 36/37 day cycle. Uggh! I'm so frustrated! I wish I could help, but I am also looking for insight!
Being on the pill can mess up your cycles until your body regulates. I would see your doc about it, they can better tell you what could be going on. Sorry I don't have more info for you, I'm not too familiar with BC.