At some point I figured out that it was all about the intestinal microbiota, so I had decent success at reducing the dysbiosis with with caprylic acid and undecylenic acid. Intestinal bacteria, even the "good" ones, sometimes produce histamine, and always produce gas. The "bad" ones produce literal toxins.
Recently I added S. Boulardii and I am now 60-70% improved as long as I maintain this admittedly difficult diet (while making sure to avoid vitamin, mineral and fat deficiencies).
My life has been hell since the age of 11. I was "drunk" and sick to my stomach for decades before the trial and error paid off. The doctors I saw kicked me while I was down. It is quite a dark realization that the industry sucks for entire classes of illness, although I do recognize its merits in treating stereotypically presenting illnesses.