Cowashing will remove dirt but it won't strip the natural oils. That's really the whole point. You don't have to scrub the roots, but you need more moisture and a daily condition will help that.
All I'm saying is that with dry hair, you're going to add more moisture than once very few weeks, and in addition, you are cruelly not using conditioner of any kind right now, you're just using a protein treatment. You need a lot of moisture to balance it out, that's actually working against you and making it worse.
I've not tried hairfinity, but I personally would try a few simple measures to add moisture before the expense of the pills. It really sounds from your description and your routine that your hair is just very dry.