What Causes A Bump On The Forehead And Swelling On The Face?

Hello Doctor, my son has been experiencing the following symptoms, a week ago he woke up with a large ( about size of a quarter) bump on his forehead, not a bruise. It was soft to touch and moved around. The next day, swollen lower lip, and itchy chin. I thought it might be an allergy, his doctor gave him some claritn. Along with these symptoms he next got a bad sore throat. He said like razor blades. Also was having some stomach upset . Last few days everything seemed to subside. Today he woke up his whole face was swollen. Lips, nose, eyes. And was having some diarrhea. His doctor gave him a referral to a dermatologist and a GI referral. I told him to take some Benadryl. He was not experiencing any breathing problems. What do you think this could be? He is 29 years old, very good shape and healthy otherwise.