my son is having a slight allergic reaction to his second hep a shot. His arm in that area is red, swollen, itchy and warm. I have given him benedryl for the itch about 3 hours ago. It seems to have helped the itch for now, but is still swollen, red, and warm. The spot is about as big a round as a tennis ball. Is there something i can use at home to treat it? Will hydrocortizone cream help?