(Question) Are there good ways to prevent and treat frequent stomatitis?

Recently, I have been getting canker sores very frequently.
Since oral hygiene is important, I make sure to brush my teeth three times a day, floss, and use mouthwash after meals. However, I still get cavities frequently, sometimes once a month in a row, and I've even had two or three cavities at once.

I never had canker sores when I was very young or in school, but as I got older, they have been occurring more frequently recently, and I don't know the reason. It's so painful that it's hard to eat food.
Famous medicine... I also tried Albolcil, but due to its strong ingredients, only the healthy skin around the stomatitis peeled off, and the stomatitis itself didn't healㅠㅠ I also visited the hospital, but the prescribed gargle medicine felt only mildly effective... It keeps coming back quickly.

Frequent occurrences are stressful, and once it happens again, it lasts for a very long time.
Starting from a small size as shown in the attached photo, it gradually grows larger and becomes completely white, with inflammation reaching its peak. Only then does the size stop increasing and, remaining in that state, the inflammation begins to slowly subside. It takes about three weeks for the pain to disappear and for the traces of stomatitis to become faint.
When a bump appears in a visible spot like in the picture, it makes me very self-conscious when talking to people, and even when I keep my mouth closed, the inside of my lips bulges out so noticeably that it looks swollen.

I'm taking vitamins B, C, and D because I wonder if there might be issues with immunity or nutrition, but is there any other supplement that would be good to take additionally?
Please let me know if you know any good supplements, management methods for preventing stomatitis, or effective ways to soothe existing stomatitisㅠ!

The photos show the process of stomatitis developing and healing in order.

(I'm sorry if the picture is too explicit and makes it uncomfortable to look at ㅠㅠ)