Sorry to add a little more here to your troubles, but, over many years I went to such doc's and only with perseverance have winkled out the answers to my problems.

Take into consideration that Hg affects the enzyme that converts T4 to the more potent T3 thyroid hormone. Therefore, taking synthroid (T4) will only have a short term affect on your symptoms before you start to wonder why you're taking these meds. The root cause is the Hg.

Parasites such as Giardia and Amoebas, depending on how infected you are, will shut your thyroid down. In fact I know of at least two doctors that treated their patients by, not prescribing thyroid meds, but by treating the parasites. They release chemicals to suppress your immune system and neurochemicals etc. Proper little chemical factories, all so they can reproduce.

The root cause of my massive infection turned out to be Hg poisoning. The Hg suppresses the immune system in your intestinal track and therefore leave the parasites to multiply uncontrollably, even with a very small exposure. My brother also suffered from dysentery, and he always lived in England, never went to far off lands. Considering these little beasties have evolved (Darwin again) they have no fear of Chlorine any longer and can readily be found in swimming pools.

Something worth taking into consideration.