have you looked into candidiasis? it is a yeast condition that grows in your intestional tract and gives off toxins. as a result of the toxins, your immune system creates antibodies to fight it off, however they end up attacking your thyroid levels as well. if you can eradicate the candida, your thyroid levels will return to normal.
there is a reason your immune system is producing antibodies, and being on medication isn't going to help any, other than cover up the symptoms and give your doctor a nice paycheck. you need to find out the root cause, address it, and then your immune system will return to normal.