Its very pain full and so much reddish in my mouth and Mouth ulcers can be painful, which can make it uncomfortable to eat, drink or brush your teeth. It's usually safe to treat mouth ulcers at home, although your pharmacist may advise that yousee your GP or dentist if: your mouth ulcer has lasted three weeks you keep getting mouth ulcers your mouth ulcer becomes more painful or red – this could be a sign of a bacterial infection, which may need treatment with antibiotics Mouth ulcers are also a possible symptom of a viral infection that mainly affects young children, called hand, foot and mouth disease. Speak to your GP or call the NHS 24 111service if you're unsure.