Suggest Treatment For Flaky Scalp

sir,i have a problem with my scalp it's flaky .whenever i comb my hair it's started to shed like white snow and also sometmes it's itching also.some doctor prescribed me nizral 2% i used it twice a week and my hair turned rough,so i stopped using it but the flaky thing is back again.is using nizral good for the scalp?should i use it twice a week?is nizral a shampoo or a scalp cleaner?
please help me with my queries.