An aphthous ulcer is typically a solitary round sore or ulcer inside the mouth on an area where the mucosa is not tightly bound to the underlying bone, such as on the inside of the lips and cheeks or underneath the tongue Major aphthous ulcer(pictured) is a type of Aphthous ulcer which is large (often more than 10 mm) and takes weeks or months to heals with scarring. The main goal of treatment is to decrease the pain and discomfort and promote healing. Credits: https://dermnetnz.org/topics/aphthous-ulcer/ https://images.app.goo.gl/nc9VgZCyDxtzb2d4A
If you are in a tight budget and can’t use medicine. Place some salt on the ulcer directly. It will sting, leave it there for a few seconds till your mouth salivates. Then rinse your mouth with water and repeat three times a day it’ll be gone the next or a couple days. I’m not a doctor but this has worked with my family and friends since salt is a disinfectant.