Wow, this sounds frustrating! Sounds like you've definitely tried lots of stuff. My first thought was to question whether your hair really likes protein, but you've already tried routine with and without it...

Have you considered trying flaxseed gel? I'm wondering if that might be a good option since I hear you can't really overdo the stuff! It's supposed to be great at taming frizz and nourishing the hair and you can get protein or other stuff added to it to customize the formula to your needs.

I'm also curious as to what your hair looks like. We all have different expectations for our hair. I like definition and volume, others like clumped curls and a more contained look. Maybe post a picture of your hair and an aspirational picture of what look you're trying to achieve?
|| 3b; normal porosity; fine/normal texture || CG since Feb 2010 || SD/dandruff prone

Current Routine BAQ henna 1/month Leave-in OH Hair Dew Cheapie Conditioner Tresemme Naturals Moisturizing
Old Stand-bys extra-virgin coconut oil Protein AO GPB; Moisture AO HR Style AOMMJ Kept for troubleshooting.
Waiting to try extra-wide curlformers SD treatment H&S Clinical Strength