Choice

Washing your hair/scalp every two weeks is not often enough. And why are there scabs? From you scratching?

Skin on the human body sheds constantly. But on the scalp, the hair tends to trap the shedding skin. I would think that your head would itch more often, but perspiration would definitely increase the itching sensation. Shampooing more often, at least a few times per week, would allow the trapped skin to be sloughed away and greatly reduce the itching you are experiencing.

If the scabs are not from you scratching your head, you should see a dermatologist.