In severe mouth ulcer attacks, you may also experience: Fever; Physical sluggishness; Swollen lymph nodes; How are mouth ulcers treated? Pain from a mouth ulcer generally lessens in a few days and the sores usually heal without treatment in about a week or two. If sores are large, painful or persistent, your dentist may recommend an antimicrobial mouth rinse, a corticosteroid ointment, or a prescription or non-prescription solution to reduce the pain and irritation. Can mouth ulcers be ...