My son's mouth was very sore. He had little white spots that looked like irritation but not thrush or even canker sores. Turned out the soreness started after he ate some beef jerky the other day.
I had him put 1/4 teaspoon of baking soda in a couple of tablespoons of water and rinse his mouth. I gave him two moist black tea bags, folded up, to hold in the back of his mouth between the molars where it was the worst. He went to work and I forgot about it. Later I asked him about it and he said it was mostly better.
I am guessing that his mouth got overly acidic and irritated. The baking soda helped reduced acidity and the black tea has astringent and healing properties.
You don't always always have to know exactly what is wrong to help a situation. Baking soda and tea will work well for so many mouth issues and is generally a safe place to start if you don't know what to do.
~Mama to Many~