I brush my teeth three times a day and use a mouthwash every evening, I always have mouth ulcers, Why?

Mouth ulcers are not caused by poor oral hygiene. The secondary infection of a mouth ulcer (which may make your ulcer last longer and be more painful) is more likely if you have poor oral hygiene. If you are subject to mouth ulcers, you must be particularly careful not to hurt yourself inside the mouth (micro lesions) during the brushing of your teeth. Oral traumas are the main triggering factor known for mouth ulcers. Finally, it is in general not recommended to use a mouthwash over a long period of time, as it may harm the floral equilibrium of your mouth and the quality of your oral mucous membranes.