Recurring multiple mouth ulcer. Course?

I have recurring mouth ulcer since since 2020...in july 2022, i had consultation with dr...he prescribed me 1 month multivitamins tablet that time...after having course of 1 month...i get rid of mouth ulcer...for 2.5 years...i have never a single mouth ulcer during.. 2.5 years...after course... But unfortunately.. In 2025...i have again same problem...every month...since jan 2025...recurring mouth ulcers (multiple 10-11 ulcers at the same time) and heals automatic within 10 days... I have noticed that whenever my stomach gets upset... After tht mouth ulcer are occuring... My question is that...should i take multivitamins course again...or there is any other problem...any problem in stomach...??? I have no pain...in stomch at all??? Only mouth ulcer Please🙏🙏 advise me...what should i do...???... Should done any test??? Or should take multivitamins course??? I am suffering from multiple mouth ulcers... It is paining lot...please help🙏🙏