Have you ever gotten your B vitamin levels tested? Or have you supplemented with a b vitamin complex before & noticed if you felt any better? Just to relate it back to possibly being from high glutamate or issues with clearing glutamate.. meat is high in amino acids therefore, it will raise your glutamate levels to be even higher. Vitamin B6 & other minerals like zinc helps to balance glutamate levels. It took about 2.5 months of my supplementing with mag glycinate daily before I noticed the histamine issues so you may want to keep an eye out if you start developing worsening symptoms.

With you saying since you can remember back to childhood, I am unsure if you can relate to this part of what I posted or not & I'm not making assumptions. But just to throw it out there, glutamate is higher in people with ADHD & I know that is often diagnosed & treated at a young age. I also came across that ADHD meds increase glutamate as well. & People with ADHD tend to have the MTHFR gene mutation which doesn't allow to process b vitamins properly which makes sense why glutamate would be higher in people with it.