Dandruff throughout year. My hai alone.

I have dandruff through out the year. My scalp is very itchy. I apply mustard oil over night twice a week, massage and wash my hair the next day. Before the application of oil I scratch my head with the help of a comb to remove the dried flakes kind as much as possible. Sometimes there is dandruff even after I wash my hair. I have tried anti dandruff shampoo and home remedies but with no luck. Also, my scalp becomes oily if I don't wash it for 3days. Due to the increase in dandruff I am having upper eyelid infection which becomes unbearable. I am concerned abt grey hair as well which might occur due to chemicals. I have been using shikakai Heena ayurvedic shampoo for years now which I dilute it before application. Also use dove conditioner for my hai alone.