Constant occipital headache

[Shilohstreams]

In 2008, I was injured in a car wreck, struck from behind at a traffic light by a car that was estimated to be traveling approx 40mph. Diagnosis was extreme whiplash but after several weeks of intensive chiropractic, I bounced back and did well until 2011. My job duties changed and working at a bench, I would look down at the work space and then upward at test instruments - I developed a headache one day and it has been 24/7 ever since. I've had bone spurs removed with C5/C6 fused, a rizotomy, bi-lateral facet injection, trigger point injections, Botox, Myo-facial release physical therapy, chiropractic and acupuncture. Some has helped - usually for  a short time - but the headaches are getting worse both in intensity & length of time.
A RN told me that some children require a craniotomy for chiari and he is wondering if I might have a developed something similar due to the wreck.

Any thoughts? I need to find a solution or at least a more effective treatment