What Causes Intermittent Swelling Of Lymph Nodes Behind The Ear Above Neck?

I have been researching about swollen lymph nodes behind the ear/above the neck area as I have been frequently experiencing an off and on swelling on the left side. It is usually only minor with little to no pain unless touched, from what I have read I am guessing that it is caused by an infection in the scalp. What is the danger of this ailment? I plan to visit a medical center as soon as possible.