B..
How often do you cut your hair? The longer you go in between hair cuts, the worse your hair gets. (I know, I'm known to go longer then a year between cuts.) What happens, is your split ends cause havoc on your hair. They begin to break up the shaft of your hair, to the root. This is what all the frizzies are. Or, if you get your hair cut on a normal schedule...do you use elastic hair ties? They cause your hair follicles to break, which makes for very unhealthy hair.
I am like you. I don't color treat, use products, or appliances on my hair. The only way I could repair my hair, was the get a significant amount cut off, and cut the ends off every 4-6 weeks as it was growing. My hair is very healthy now.