Hello and welcome to hcm forum,
Mouth ulcers can be of aphthous ulcer type.
Such ulcers are usually caused due to-
Poor oral hygiene
I would advice you to get a thorough clinical evaluation done by a dentist
Avoid anxiety and stressful jobs.
Maintain oral hygiene well.
Take fluids and nutritious food.
Vitamin becosules,iron and folic acid
tablets can be administered.
In severe cases,corticosteroids
has to be administered.