hi. you could be having seborrheic dermatitis
of scalp or may be Scalp psoriasis
. sometimes it can be stubborn and recur.
Use a coal tar
based lotion like Ultitar-CS lotion once daily in the night or on alternate night and apply in the scalp skin with fingers. use it for 2-4 weeks
Use a coaltar based shampoo like Protar shampoo.
continue using shampoo for maintaing improvement