It can take several months to figure out the right dosing with thyroid meds because you have to go back and retest every six weeks or so. Doctors tend to be VERY conservative with thyroid meds too, so I'd stick to the ND for that, they usually treat until your symptoms are resolved, not just treat to a number from a test.

http://stopthethyroidmadness.com is a great place to read up on thyroid disease.

It is worthwhile to stick to your diet even if you're not losing because the other option is to gain. So, hang in there and persist in getting your thyroid issue well-managed. It can be about impossible to lose if you're still hypothyroid, but you certainly don't want to gain more, right?