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).
There is nothing on my scalp, so I know that it is internal. It burns and my scalp tingles in that area almost making my scalp itch, but I cant touch it. I have recently been sick with a sinus infection and was told I may have an infection in my sinuses on the back of my head. It is really painful.