Hello,Sodium lauryl sulphate (SLS), a common toothpaste ingredient, can also cause canker sores. SLS is a soft tissue irritant found in shampoos, soaps, and cleaning supplies. Because it causes foaming when we wash our teeth, companies utilise it in toothpaste. It can be due to Vitamin C deficiency.

Hi. I can totally understand the kind of discomfort you're feeling. As you've said, the vitamins you're taking for 3 days, it would take sometime for the body to gain the deficient level of the vitamin back. In the meantime, please look into your daily lifestyle and if there's an increased stress level as well, stress can also cause ulcers. Also include citrus fruits in your diet to compensate for any vitamin c deficiencies. Ulcers generally tend to heal within 7 to 10 days depending on the size, larger ulcer will take more time. Rinse your mouth with lukewarm water and a pinch of salt a few times daily till the ulcer heals.