The doc is much better than even many endocrinologists. Even though B12 wasn't mentioned, it sounds like he is the type who would be willing to learn. Here is one good article: http://www.aafp.org/afp/20030301/979.html You might want to make a copy and give it to him. There's much more to the issue, but the article will provide him with a good background knowledge.

One possibility with thyroid is Hashimoto's, but I imagine that your doc would have caught and mentioned that. Do you have copies of all your records and lab results? A very good thing to do, to get them and keep your own set of records.

Please keep asking questions. Let me know if I'm still not clear.

rose