You may not realize you have a neck issue. I call them subtle neck injuries. The only symptom is headaches. Imaging does not show any abnormality. They cause some muscles to spasm that lead to headaches. If you have a headache and the bony spot behind your ear is tender to the touch, you also have a neck muscle spasm. It can be the cause of your headache. Those 6 month headaches could be a 6 months before the neck stabilizes muscle spasm that triggers a headache.

When you have a headache, try icing your upper neck on and off for a few hours. I worked for me most of the time. It helps to get the ice started early, before things get bad.

As Dr Marshall in the Concussion vs Whiplash YouTube explains; Whiplash can be triggered by very light forces.