Once you have an annoying mouth ulcer you can try to rid yourself of it by
1) Taking a anti-biotic tablet (any anti-bio tab) pulverizing it and mixing it with honey and applying on the affected area .
2) Try applying glycerine to the affected part .
3) There is a gel by name "Dologel" available at all leading chemists over the counter , use that .
If all of the above fails then , its hard luck . You will have to grin and bear it for 1 week or so till it disappears as smoothly as it appeared .