Hi..
Welcome to HEALTHCARE MAGIC..
I have gone through your query and can understand your concerns..
As per your complain it seems that you are suffering from Seborrheic 
Dermatitis leading to the symptoms of 
dandruff, extremely itchy scalp and sore spots on scalp..
As it has recurred there is a possibility that the under lying factors that can commonly cause it like 
fungal infection, stress etc have not been taken care of or there is a possibility that the previous infection did not cure completely leading to recurrence of infection..
I would suggest you to start washing your scalp every alternate day with shampoo containing 
Ketoconazole, 
salicylic acid, sulfides, coal tar, selenium, zinc..
Massage the scalp with a steroid lotion as it will also help in relieving itching.
You should also keep the scalp clean and avoid moisture accumulation..
You can also apply Yoghurt to scalp..
Drink plenty of water and maintain a good scalp cleanliness..
Hope this information helps..
Thanks and regards.
Dr.Honey Nandwani Arora.