One of the main causes of sinus drainage is simply being alive. Every day the human body produces several liters of sinus fluid and mucus, and all of that natural liquid must go somewhere.
It is a area of tenderness of the scalp in which people also sometimes feel stabbing headaches. Others just feel very sore and tender to the touch. It is felt to be caused by irritation of the connective tissue which attaches the muscles of the scalp to the skull (cranium).
The burning pain in the scalp can be due to several causes like occipital neuralgia, cervical migraine, localized patch of dermatitis or eczema or even dandruff and even due to infection in the underlying bone. A medicated shampoo will help only if the pain is related to dandruff.