Labs to run: Look for low levels of T4 and T3 despite a normal-to-low TSH. Also consider viral labs, such as Epstein-Barr virus (EBV).
What to do: I recommend natural brain-immune support tools, such as astragalus, olive leaf, rubidium, sage leaf, L-lysine, zinc, and vitamin C. For more recommends, read "Signs You Might Have A “Leaky Brain” + What To Do About It.