I have had a simalar problem that started a month or so ago and that was the same time I started taking the vitamins. I only take one flinston vitamin for kids the chewable, my dr recomended because I was having a problem with the prenatal vitamins making me sick...I does hurt with some foods but always with the vitamins...The way the dr above describe a canker sore is kind of what mine looks like but I have never experianced one so large.
Mouth sores may be symptoms of a disease or disorder. It may be due to bacterial, viral or fungal infections. In particular, Canker sores start with small ulcers with a white or gray base and a red border that are found inside the mouth. Their exact cause is uncertain but some experts believe that immune system problems, bacteria or viruses may be involved. Fatigue, stress or allergies can increase the likelihood of a canker sore. They usually heal on their own after a week or two, but an outbreak may occur. Over-the-counter topical anesthetics and antimicrobial mouth rinses may provide temporary relief. Antibiotics can reduce secondary infection. Stay away from hot, spicy or acidic foods that can irritate the sore. It is possible that there is a secondary infection involved. But it is best to see the oral surgeon for further evaluation and management. Food allergy does not usually present with blisters. What vitamin and what dosage were you taking?
Take care and keep us posted with your appointment.