Mouth ulcers can Persists due to number of reasons.it might be because of toothpaste, vitamins deficiency,stress ,bacterial or viral infection.
Apply dologel before eating food.take B complex tablets once a day for a week
Next Steps
if it still persists ,please visit a dentist
Health Tips
take a glass of lukewarm water ,put a pinch of salt and gargle with it 3-4 times a day
have less spicy ,soft food which is brought at room temperature
drink adequate amount of water and avoid citrus fruits, caffeine intake