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).
My scalp started hurting a few days ago and its really uncomfortable. Its around the crown of my head and its worse a little toward the right side, but anyhow, it hurts all over my scalp. Im not sure why... but I looked it up and apparently Im not crazy. But the thing that stood out the most to me was a few articles about substance P causing over-sensitivity.