I think the doctors should have tested your thyroid before the lithium if they didn't....and while taking it you should have had regular blood tests to monitor thyroid and other things.

Take for instance birth control pills. I'm a smoker over 35 and was warned by previous Gyno's about the stroke risks associated with birth control and my risk factors. My current Gyno wasn't going to warn me about it which I consider negligent. I should quit smoking but it's not that easy and the fact that I'm a smoker shouldn't mean I receive less considerate care, just as obese people should not get negligent care because they don't diet.

As I stated, I'm not a doctor but I do worry you either had the thyroid issues to begin with and now that you no longer have a thyroid and the hormones running through your body are synthetic, you continue to have symptoms. Or, you had risk factors for thyroid issues and it should have been discussed prior to making a decision to take it. If it's health related, a mental illness label seems excessive. This is how I would feel if it were me, you probably have experiences which differ. No matter how it happened, I'm sorry.