Hi. I'm a bit over four years since my retrosigmoid surgery for a 3.0+ cm AN. I too have bizarre but excruciating pain at the incision sight. This is not a headache/migraine per se, although I get those too. This is pain to the touch of, I guess, the mastoid bone. It's not constant but when it happens I cannot touch the area. If I roll over in my sleep onto that side of my head, the pain will actually wake me up. I have described this to my primary care doctor, my neorologist, my ENT, and they cannot explain it, do not know what it is, do not offer any theories about what it might be, and have not pursued it.
Part of what I feel is as you describe: tightness and pain near the incision site. It becomes very sensitive to the touch. Yet, at other times, there is no pain. I can feel around, wash my hair, brush my hair, wear glasses and the sensitivity, tenderness, and pain is gone. At other times, I cannot touch it. I have no explanation for this and haven't noticed a consistent pattern.