Firstly do they heal and reoccur in different places or same? If they don’t heal or keep happening in the exact same place show a dentist.
Looking at your age and location of ulcers I’m guessing it’s Aphtous ulcers . There is no one reason for them . Main causes are Stress , Dehydration and
Vitamin B12 deficiency. Most common one being stress.
Next Steps
Take
Vitamin B12 supplements for min one month. Once a day .
Sports or meditation for stress
Dologel CT for relief from pain
Health Tips
Had read an article that brushing over them can bring the healing time down to half (very painful though)
Some of my patients found it helpful.