Before I was diagnosed and all through my adjustment to med period, my tongue burned constantly. My mother was hypothyroid, too. For years before diagnosis, she perceived a salty taste in her mouth. She may have actually been sensing that burning feeling and had equated that with the burn that salty foods make, more so than the actual taste of salt... but I'm just guessing. Individual brains perceive the signals from far away nerves in individual ways.
The soreness - and sometimes swelling - has to do with a build-up of muccopolysacharrides in the tongue and other tissues that happens with hypoTism. You may see ridges on the perimeter of your tongue due to swelling. You may even bite your tongue more often while your thyroid levels are low.
When I told my present doctor about the burning, he said he hadn't heard of that being a hypo symptom before, but he thanked me for teaching him
something. How cool is that?!? He's an
doc. My mom consulted at least 4 doctors and a dentist about it; they all told her it was in her head. The final one she saw told her to see a psychiatrist. She was the kind who believed in doctors instead of educating herself, so she finally gave up and lived with it until her thyroid failed enough that she was finally formally declared hypo.