Hello, My Son Is 4 1/2. He Is Small For

Hello, my son is 4 1/2. He is small for his age (30lbs). Lately he is randomly getting high fevers (102) and headaches. Crying for no apparent reason. He has started complaining of pain in the tummy while urinating, and is peeing in spurts. He has mild swelling near both temples, one worse than the other, right above the ear, like a goose egg. Vascular maybe? Could it be worse, like something devastating?