Are you confident in the thyroid results? Do you know which tests they ran and what the numbers were? Sometimes test results are "normal" but close to the end of the range, in which case they're not reliable because of the standard error involved in any test. I mention this because I've had a lot of experience with measurement problems, in greyhounds and in people. When our Spencer got aggressive, it was because of thyroid, but the screening test was technically normal. (His T4 was 1 on a scale of 1 to 4.) Knowing what I knew, I requested the full thyroid panel, and it turned out he wasn't normal after all. The "aggression" was really a reaction to feeling vulnerable and it stopped as soon as the medicine was begun.
You'll be lucky if it's that simple, of course, but it's far from rare. In any case, you have my sympathetic concern and support. It's a situation that's scary and confusing!