I'm pretty sure it's genetics. Last time I got my hair cut was in early December, 2010. I started out with a business man's side part haircut, and my hair is now down at collar length, doesn't even touch my shoulders. Hair is mostly protein, but I take protein supplements and vitamin pills because I work out 2-3 times a week, and that doesn't seem to affect my rate of hair growth.
I'm fairly sure that lack of sleep affects every body function, so your irregular sleeping habits probably don't help, but the root answer is probably still genetics.