is common. Toothpastes with sodium lauryl sulfate can contribute. Can be caused by viruses. Auto-immune processes can cause these. Anbesol type products may help. Ocassionally tetracycline
is used either topically or orally to help. There are "magic mouthwashes" that help (mixtures of antihistamines, maalox, steorids, others). See pcp if not resolving.