What causes mouth ulcers all the time?

It depends: Mouth ulcers could be due to systemic or local reasons . Get a checkup by your dentist and give him a detailed medical history to see if the mouth ulcers reflect an overall systemic medical problem . They could be peptic ulcers

Stress: Stress can be acidic foods, trauma to tissue, too much sunlight, physical stress and emotional stress. There are medication(s) that will reduce the severity and duration of the lesion(s), but is mostly for palliative care. To my knowledge, there is no medication that can be taken to prevent the occurrence. Just moderate stressors, if possible.

Canker sores: are the most common oral lesions. Individual ulcers typically last 1-2 weeks. The condition is idiopathic (cause is not known) recurrent aphthous ulcers is usually self-limiting. Try to keep adequate oral hygiene as possible. If concerned see your dentist after 10 days or visit today for laser immediate amelioration.