What Causes Crawling Sensation On The Scalp?

In one area of my scalp, one specific spot, I feel as if there is a bug in my hair moving but when I look there is nothing there and it stop almost instantly stops when I touch my scalp in that particular area. I remember it starting almost 2 years ago but never really noticed it as much as I have lately and the past few days it has been constant roughly every 10 minutes or so. I cant tell if it is on my scalp or buried under the top layer of skin but it is starting to irritate me. What could it be and what should I do?