So this is a new one, even for me.†
Salivary gland stone. Who knew that you could get stones in your salivary glands?! Apparently this is a residual side effect from the treatment last summer for thyroid cancer.
You may recall, after they removed the thyroid, the treatment to kill any leftover cancer cells was swallowing a pill of radioactive iodine. The main side effect from that, aside from potentially contaminating people with radioactivity, was swelling of the salivary glands leading to dry mouth.
The salivary glands usually take a little while to fully recover, and mine have never truly returned to what they were before taking the pill. Dry foods such as crackers or pretzels still turn to dry, pasty dough in my mouth.
So the lack of saliva production can lead to, you guessed it, a stone in the gland itself. Luckily, these types of stones can often dissolve simply by stimulating saliva production. Recommendations to make that happen so far have included sugar-free gum and lemon drops.
The gum seems to work best, but others have suggested li hing mui or lemon peel. If you have any others, feel free to leave in the comments!
† - Up until now I didn't think anything could top iritis for ailments I've actually had that sound made up.