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).
If you have ever had a hangnail, you probably know what a paronychia feels like. Paronychia is an infection around the fingernail in one of the folds around the nail. The skin fold swells and becomes tender or reddened. Sometimes a pocket of pus accumulates which creates more pressure against the edge of the nail and it becomes increasingly tender and sensitive to touch. Even a band-aid can be painful to apply.