Well, if I could give you a 100 likes, I would do so. I'll try this to see how it works out. You say a month or two of stretching does it, eh?
Also?!?!? Try a hot shower, really hitting everything from the top of the head to the bottom of your shoulder blades, and around to your jaw and collarbone. (Think of it as the Quick Oats version of a trapezious stretch.) (I realize suddenly, this amounts to "Oh go soak your head!"......)
Second the computer/gaming glasses. I had the exact same symptoms as you for years with all the same negative tests. I bought a pair of gunnar glasses and I've worn them for 3 years with a dramatic decrease in headaches. A friend of mine who's a software developer turned me on to these and they have literally been a godsend. https://gunnar.com
Sorry to hear about your headaches. I use f.lux software. It filters out blue light in the evening, to prevent the disruption of my Circadian rhythm, for better sleep. It can be used during the day, as well. It is free, and works very well. https://justgetflux.com/
I just downloaded. Thanks, man. Will certainly try it. Though based on harami's comments, it might be the muscles in the upper neck.
I could rattle on at length about fluorescent light sensitivity so I would be the last person to downplay that. However, the sinus problems cause me to suspect that some type of allergy could also be at play. Many people who have this kind of office related sinus problems and headaches are - for example- allergic to chemicals in the air from the photocopy machines. Very common- but just an example. Just sayin, allergies are another avenue to look at as you experiment. Could also be dry-air from low humidity during winter months when the heat is on which would aggravate your sinus condition the longer you are in the office. And once your sinuses are aggravated the headaches and nausea can follow. Things like that. ditto on the f.lux too.
Harami was bang on with the cause. Have been doing the exercises he recommended, and going to massage therapy and chiropractor who also confirmed what he suggested (granted, they will confirm anything they service, right?). A couple weeks later I still have the ear plugged sound, but no more headaches. And the ear plugged issue is getting better. THANK YOU, Harami.