itching on my eye brow,white powder falls down from hair

Hi this ravi, I have some serious problem with my Head scalp hair, i have lots of dandruff in my hair and sometimes i also keep loosing hair, its itching even on my Eyebrows and a white powder starts falling down from hair when i start combing or scratching.Six moths back i met a dermatologist he gave me a shampoo called sebawash 2%, and a tablet called Zimig (Terbinafine Tablets) i continued for 6 weeks it worked well and i had no dandruff. I was happy that i am out this problem but then after 1 year i started getting the same problem still have the same issue please help me . Suggest me something where i can come out permanently.(I am 28 years old).