I Occasionally Get A Sort Of Mildly Throbbing Pain On

I occasionally get a sort of mildly throbbing pain on the lower left hand side at the back of my head around skull bones. Over the last few days it has become more noticeable, including since yesterday followed by a massage. I wonder if the pain is due to muscle tension (I usually carry muscle tension on the right hand side of my neck and upper left hand side of my shoulders), or if it is something more that I should investigate?