My scalp is very itchy even though i use an anti-dandruff/itch shampoo. it is itchiest on the crown and back of my head.

May not be dandruff: If it is getting worse with the dandruff shampoo it most likely isnt dandruff. You should get it checked out by a dermatologist

DHS zinc shampoo: You may be dealing with a skin condition a bit more severe than simple dandruff. DHS Zinc shampoo is an over the counter shampoo that helps many people with conditions that cause severe itching, such as psoriasis.