@ristu I had mouth sores on each side of my mouth at the back of my teeth (inner cheek sides) and yes, the Vit. B12 did take them away. When I eat something very acidic, I get a slight soreness, and it goes away soon. While I'm not allergic to Walnuts, Raw Pineapple, and Strawberries, they do affect my mouth and make my tongue sore, as well. Years ago, I developed a very sore mouth and tongue from taking Vitamin A and coincidently, or not, my mouth sores came at this time too. While taking the Vit. A, my mouth was so sore I couldn't eat very well. My sister, who also takes supplements for Fibromyalgia, said she had the same symptoms when taking Vit. A.
I urge you to check out a Naturopath whose medical practice also contains information on vitamins, foods, and body depleted hormones,, etc.