What Causes Very Red Swelling On Ear?

My 7 yr old son all of a sudden has a very red swollen left ear. He mentions no pain or itch, but he did say it feels warm like a sunburn. There is no mark indicating an insect bite but the top rim of his ear is definitely very swollen and his ear clearly is sticking out from the swelling. It is Friday night so I am wondering if I can wait this out or if he should be seen immediately? I did give Benadryl just in case it is an allergic reaction but it did not seem to make the swelling go down.