If your hair if very oily gunk collects on your scalp and causes itching. My solution was to scrub my hair every day, using a castile soap. I guess a detergent soap would work too. Just wash, wash, wash
Dandruff can cause either an overly dry scalp with itchy white flakes that may be waxy or greasy, or it can manifest as an oily scalp with scales. Eat a healthy diet. You can also take vit B6 and vit A and E which are good for hair and skin. Try medicated shampoos for dandruff. There are a number of over-the-counter shampoos available that can help. The most effective ingredients -- antimicrobials -- to look for are zinc pyridinethione, selenium sulfide, sulfur and ketoconazole (also available by prescription). If your hair is colored, don't use products with selenium sulfide or sulfur.
If the symptoms persist please consult a trichologist for the confirmatory diagnosis and treatment. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.