Thanks for asking the query,
Frequent mouth ulcers is aphthous stomatitis occurs due to many reasons few are;
Nutriotional deficiencies like vitamin B & C , folic acid
Immunological imbalance, hormonal diturbances,
Allergic reactions, trauma from broken or sharp tooth.
Stress, consumption of tobacco or smoking.
I would suggest you to visit to Dentist
and get the checkup done.
Apply cortisone acetate
oral ointment topically over the affected area.
Use lukewarm saline gargles 3-4 times a day, and natiseptic mouthwash gargles twice daily.
Avoid eating of hot nad spicy foods.
Hope this helps out.