My son has strange welts that are raised on his back and tummy. they flare and calm periodically but can look very big and angry. what could they be.

Itchy?: I think what you are describing are hives which can usually be controlled by taking antihistamine . The cause if often obscure but allergy to food ,drug, and viral infection can induce hives. If they last more than 6 weeks, they are classified as chronic - about 30-40% are considered autoimmune, the rest is often unknown, If they don't itch, the diagnosis needs be reconsidered.