Comment by Asooka
It is possible you have an undiagnosed latent infection, I spent nearly a decade with one trying this and that until I hit a winning combination. If you go looking for this protocol you'll find the absolute worst schizo rants online, but the actual ingredients have solid science behind them (you can literally look them up on google scholar):
The N-Acetyl Cysteine Protocol Morning and Evening: 600mg NAC Oregano Oil (min. 40mg Carvacrol) Black Seed Oil (1 teaspoon)
For the natural oils, my strategy is to mix 235ml Nature's Way Black Seed Oil with 30ml Natural Factors Oil of Oregano, take one teaspoon morning and evening. This mix delivers the prescribed amount of carvacrol per teaspoon. Most of my problems were with the upper respiratory tract and taking it orally this way coats the throat well.
The other intervention that had big effect on my health in the last few years was adding a daily mineral supplement. I'm an avid tea drinker and it turns out that can interfere with your absorption of minerals, plus with the nutrition crisis it is not clear if our produce even has enough for optimal health. I simply take the maximum recommended supplementary dose of Mg, Ca and Zn.
Also, check your Vitamin D levels if you haven't. If you have been dealing with this for 12 years, I assume you have already ruled that out, but I'm mentioning it for completeness. Good luck.
P.S. One last thing to mention - try the carnivore diet for a bit (if you haven't, of course). I know people who have found it a big help, but then again for some it didn't do anything. Give it a month, see how it goes, obviously stop immediately if you get serious symptoms.
Thanks for the suggestions. I've done extensive trials with the minerals and vitamin D, and both hair and serum tests keep saying that's not the problem.
I'm on NAC too, but oregano oil gave me the worst heartburn I've ever had in my life. Do you think the black seed oil might neutralize it on that front?
I did carnivore for about three weeks before my body was absolutely shutting down. It was catastrophic for me. I did spend 20 months on an elimination diet of slow-cooked meat and boiled vegetables (exclusively, without a single cheat, which was pretty brutal), which helped clear up some intestinal issues that were misdiagnosed as ulcerative colitis, but it didn't do a thing for the headaches.
It's somewhat reassuring that most of the out-of-the-box suggestions people have are things I've already tried, because at least it does confirm for me that I've done a decent job of covering my bases, but alas, the pain persists.