Stress in itself is a killer in every way possible, however I am pretty certain that the trauma I went through as a kid has caused the development of Hashimoto's. Even reading books like 'body keeps the score' they mention how people who experience extreme trauma as a child are more likely to develop mental health and autoimmune illnesses in the future. Your body is basically attacking itself as a possible coping mechanism to the trauma, how crazy is that?
Anyway, I've noticed when I do not deal with that childhood trauma in a healthy way, my health immediately declines, my thyroid starts to swell and I start feeling hypo again. BUT when I put my mental health as a number 1 priority, where I attend EMDR therapy and counsellors who specialise in trauma, the symptoms subside and my body is not as stressed thus my thyroid isn't struggling.
I guess what I'm trying to say is, if those autoimmune diets aren't working, or changing your medication is making you feel worse, then maybe it could be down to your past trauma that's been undealt with. I'm not saying this is the case for everybody, but I've spent the past year stressing over something that was right under my nose the whole time. Remember the mind and body connection, only have the healthcare system just recently recognised this connection.