I was wondering if lack of sleep can stunt growth as some nights I will get 11 hours and others I will get 6?
A persistent lack of sleep can interfere with your body's hormones, including those involved in growth. Missing a few hours here or there isn't a problem, but if you are constantly sleep deprived that can be a problem [http://kidshealth.org/en/teens/sleep-growth.html].
I suspect you are trying to do with too little sleep on the nights you only get six hours of rest and then crash to make up for the lack. Whether it effects your growth would be hard to say, but it isn't the best way to at your peek functionality.