I spent months figuring this out, but after $2000 and a lots of docters I was diagnosed with Hashimotos. They usually do not check for that, so maybe you could ask them to test for "Thyroid Antiboddies". They get triggered by a complex mixture of an underlying viral infection and a decreased immune system (stress in other words
) What also helped me a lot was diet changes and lifestyle changes.
I would really suggest you keep on testing. I just was not happy with what the doctors were telling me so I kept on searching until I found an answer. It was a very expensive journey, but at least now I know what went wrong.