It looks very much like canker. The lesions will accumulate more cheesy substance if untreated, requiring scraping out to keep the airway clear. Hopefully, you can find the copper sulfate and treat before it gets that bad.
I also am suggesting you try to locate some copper sulfate. It can be safely used to treat canker when other meds may not work. Here's the recipe.
You offer it as the only water source for four days.
2 ½ liters of water
1 teaspoon of apple cider vinegar
1 gram of copper sulfate