I do pay fairly close attention to food intake and rarely eat out so MSG is most likely not a culprit. Also maintain a reduced refined sugar diet. I had not considered a histamine association so will research that more.

Periodically I have had "episodes" of almost complete remission of symptoms that have lasted an average of 1-3 days but these are becoming rare now and the symptoms are becoming more relentless. So it does appear to be systemic. I've had antibiotic treatment in the past but well over 10 years ago was the last time. No statins. For B-12 they tested m-malonic acid or MMA serum which I've read is a highly sensitive test and the result was 0.11 umol/L in a range of 0.00 - 0.40.

After reflecting on any new changes to my regular diet or medications preceding the onset of symptoms there was one change. Just shy of a year before symptoms I switched from topical testosterone replacement therapy, to treat low testosterone, to intra-muscular injections of generic testosterone cypionate simply because my insurance company no longer covered the extremely expensive topicals. Doctors nix any association but I'm left wondering and considering discontinuation as the test.

Yes, I wound up here due to dissatisfaction with local doctors. After completing basic diagnostic testing for the most common causes they are now more then reluctant to pursue any further diagnostics, in fact they have directly declined to do anything more in that area.

I will look further in to DNA testing as you suggested, I'm familiar with 23andMe from working on my family's genealogy but did not do any DNA testing. I very much appreciate your input here, thanks.