Zero waste shampoo, alternative for shampoo bar. Hi people!

I'm very new to the zero waste community and still trying and learning. 
I have used shampoo bars now for some time and although I really like the concept, my hair and scalp think otherwise. It leaves my scalp very itchy, I get bumps, flakes, everything. Now I bought a shampoo bar without SLS and only natural ingredients, but even that seems to be too aggressive for my head. 
The times that I borrowed liquid shampoo from friends, my hair and scalp was a lot better.

So what options do I have here? Is there a way to get liquid shampoo zero waste? Or maybe some reusable bottles? Shampoo in glass bottles? Please tell me!

Thanks!!