Talk to your local pharmacist re over the counter remedies. Bonjela seems the most likely solution but other mild anaesthetics which you apply to the ulcer may be available. Meanwhile a mouthwash of tepid water with salt, maybe after meals, or before bed, can help. Also paracetamol or Ibuprofen tablets, taken in accordance with the directions on the box can take the edge off the pain. Also helpful at bedtime if the ulcer is stopping you from dropping off to sleep.