What Causes Arm Swelling, Soreness With Redness?

My 83 year old husband has a very sore, red, puffy left arm from below elbow to wrist. He has no wound or did nothing strenuous to cause this. He is taking bloodpressure meds, Avodart, and a sleeping med. For two days he hasn't eaten anything but watermelon, milkshakes and orange juice. Has doctor appointment on 8/24....should he go sooner? What could this be?