Medical update... Just got back from the doctor, where I got a bit of an education. There were two results from my blood tests that were definite indications of a problem.
First are the levels of two thyroid-related antibodies: they are (respectively) 200x and 1,500x normal. Yikes! Basically, as she explained it, that means my body is eating my thyroid – an autoimmune problem. My pituitary gland is reacting to that by increasing its stimulation (through a hormone) of what remains of my thyroid, and under that increased stimulation the remnants of my thyroid are producing hormones at levels that are borderline low. This is called Hashimoto's Disease, and about 5% of all people will get it at some point in their life. It's easily treatable with a daily oral dose of levothyroxine, which I'm starting immediately.
Second, my blood levels of vitamin D are significantly below normal. The doctor had no explanation for this, but typically it's caused by a dietary deficiency. So I'm taking massive supplements for a couple weeks, then daily normal dose supplements after that. We check again in six weeks to see if that was all it took to get my levels back to normal. When we discussed my diet, it seemed like I ate plenty of things with vitamin D in it – so we're going to look at the results in six weeks carefully, and if the vitamin D levels don't pop back up she's going to start looking at things that might prevent my body from absorbing the vitamin D. One thing that struck both of us: my pernicious anemia (diagnosed about 25 years ago) is a condition caused by my body's inability to absorb vitamin B12. We're both wondering if there's some related condition with vitamin D...
Both of the above problems have fatigue and sensitivity to cold amongst their symptoms. Hashimoto's Disease has as a risk factor the presence of other autoimmune diseases (which pernicious anemia and Raynaud's Disease, two conditions I've been diagnosed with, both are). Both are also easily treated. So basically that's all unsurprising (except to me!) and relatively good news. And if the treatments work as advertised, I'll certainly be happy to have the symptoms reversed!