I attended a headache/pain conference this May. One of the example cases of hard to diagnose was chronic headache, in a woman over 40.
It was given as an example to doctors there to have a chest X-ray done with the workup FIRST. In some cases a problem in the chest can refer up the vagus nerve and give severe long lasting headache. So if you haven't had a chest X-ray, I'd get one. They are not expensive, or complex.
Another cause can be Medication Overuse Headache.
http://www.neurology.org/cgi/content/full/66/12/E43
http://www.neurology.org/cgi/content/full/60/10/E8
Basically I learned that a chronic headache should be evaluated by a neurologist with imaging and other tests.
Headache is one of the most complex and frustrating things to diagnose.
Best of luck.
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All truths are easy to understand once they are discovered; the point is to discover them.-- Galileo Galilei
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Weezie looking at petunias 8.25.2017
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