Hi dear , As per your query you have mouth ulcers specially at the back side of your mouth . Well there can be many reasons for ulcer in your mouth like canker sore , cold sore , inflammation of taste buds due to allergic reaction or irritation due to any acidic or spicy food , dental infection and ulcer due to acidic reflux . There are rare chance that it is cancer , so there ois no need to panic . But in your case it seems to me that the probable reason for ucler at back of your mouth , which occur mostly due to irritation due to acidic food or acid reflux , acidic or spicy food , allergy due to certain food like sea food and nuts . I would suggest you to avoid hot , spicy and acidic food , consult oral pathologist for proper diagnosis . Doctor may refer you to gastroenterologist . Hope your concern has been resolved. Best Wishes, Dr. Harry Maheshwari