Im going to have to respectfully disagree with you on the issues related to B12. The amount of B12 gained from gut bacteria is minimal at best and then only under ideal circumstances.
There are over 60 gene abnormalities that can affect B12 and methylation to varying degrees. This abnormalities can drastically increase a persons need for B12...in all honesty there are many gene abnormalities that effects enzymatic processes for nearly everything which accounts largely for why one person may need a small amount of a nutrient but another person may need significantly more.
Its good your on B12 injections, but as I just eluded to many people have found that the "normal" B12 injection protocols still were not adequate to meet their needs. Also make sure you are not taking cyanocobalamin as your injectable, its nearly worthless for most people.
LOL, you dont have to try and defend you choice to not eat meat to me, I could care less, however arguing with me about true sources of B12 and using friends who are meat eaters and are B12 deficient proves nothing other than you are getting defensive about your choice not to eat meat.
A persons toxin levels play a huge role in how nutrients are used in the body, B12 for example, is very susceptible to heavy metal binding and once bound to a toxin is flushed from the body. A person can have normal B12 intake levels but if highly toxic can actually be deficient because its all getting flushed out with toxins.
At the end of the day B12 may not be your issues, but its only one piece of the methylation cycle and people with a poorly functioning methylation cycle often have many of the same symptoms as those with poor thyroid function and of course many with poor methylation also have poor thyroid function.
What I am seeing more and more of here is people who return to this forum after supplementing with iodine/selenium for some time, make some initial improvements but then backslide or fail to improve further. This is almost certainly due to other nutritional shortfalls and simply adding more and more Iodine is not the answer.