Posting a much belated follow-up:
My parathyroid tests, h.pylori test, and celiac screen came back normal.
I just went back in for a vitamin-D retest. Taking 1800 IU vitamin D/day I was able to stay in-range. (1000 IU/day doesn't cut if for me). I suspect that I have lactose intolerance, so I probably wasn't getting enough vitamin D from diet.
Strangely enough my three sisters all seem to have vitamin D deficiencies also, so maybe it is genetic. Though one sis probably doesn't get enough sunlight due to long work hours, another may have celiac, and one is hypothyroid like me.
I have to admit I have more energy and less migraines on vitamin D, even though my thyroid levels right now are a little lower than where I normally like them to be.