Hey there... I think andrew answered most of the questions. Certain foods are very acidic. They will cause blistering and pain. stick to soft, non acidic foods, thickish and milky - easy to swallow and tolerate. This will help immensely.

My advice on the ulcer CLEAN IT... After each and every meal. Brush your teeth with a gentle toothpaste (I use a mild mint one - children's prevident or something like that - it's made by sensodine - it helps build enamel and is not too strong a mint so it doesn't burn. Follow up with a waterpik on low, and filled with lukewarm water - to rinse away anything left in your mouth.. If you don't have a waterpik then rinse with the salt and baking soda water mixture and don't put anything else in your mouth. Do this after each meal and or drink. This will clean the area and facilitate healing. There is also this great oracort gel that thickens and dries and helps heal. Maybe you can get a prescription.

take care.