There is often a lot of confusion about pain in the back of the head. Is it referred pain? Is it a headache? And to some extent in depends on who you ask, but really should look again a little more closely at the anatomy of the Innovation of the back of the head to better distinguish where the problem is, in order to have a chance at resolving the problem.
There are a total of four peripheral nerves that cover the back of the head from the midline to just above the ear: the third occipital nerve, very close to the midline, and not often a big player, the greater occipital nerve, slightly lateral to the center and often an intense source of referred head pain, the less occipital nerve, slightly more lateral, in the auricular nerve, just behind the ear and often feeling like it's deep in the bone.
All of the four nerves that cover the back of the head or originate from the upper cervical spine from C3 all the way to the occiput. What is less understood is the fact that they have to exit through a variety of myofascial paths, including fairly lateral behind the big SCM muscle. As a result, posterior head pain can be referred from the spinal articulations themselves as well as a variety of myofascial structures. Differential diagnosis of posterior head pain requires a careful examination of the structures from the spine all the way to the exit points at the nuchal line. Cervical misalignment, facet syndrome, facet degeneration, muscle spasm and muscle scoring from injuries all can be accounting for the chronic posterior head pain. It takes some detailed palpation to tease them apart. In particular I feel that a lot of the SCM muscular injuries from things like whiplash are often the source of posterior head pain but often get missed because the myofascial entrapment is likely more to decide than the referred posterior head pain.