Tell me if you ever figure this question out. I've been using Jason's tea tree oil shampoo, but it is not nearly as effective for dandruff as the "clear" shampoo line my sister uses. But the clear line has sulfates in it, so I was told not to use it. I'm going to ask my doctor I think
Tea tree oil is great for dandruff. I would recommend doing scalp treatments, possibly as a pre shamopoo treatment, with a carrier oil of your choice (coconut, olive, jojoba, sweet almond, etc) and drops of tea tree oil which can be bought at health food stores and online. Look online for an exact recipe though because you don't want it to be too harsh. There are also sulfate free shampoos that contain tea tree oil, such as trader joes tea tree tingle shampoo and giovanni tea tree triple treat that are great low poo options
You should probably see a dermatologist. Dandruff is a medical condition that needs to be professionally treated. Also Head & Shoulders is a pretty harsh shampoo. You maybe can find another cleanser that's less harsh and will help your dandruff too.