When you do sew ins, what style are the braids in (vertical or horizontal) and how tight are they?
When you wear a quick weave, how is your hair styled under it?
How often do you wash and dc?
Do you wrap your hair at night?
How often do you moisturize?
From just what I read, maybe your hair doesn't like being confined with the braids. Since that's all you do, and your hair is obviously breaking off, my conclusion would be that your hair doesn't like braids. Have you tried other protective styles like french rolls, buns, twist outs, phony ponies etc?