My 33 year old son started chills, fever, generalized aches and pains yesterday afternoon, somewhat controlled with alternating between Advil and Tylenol. He felt better this afternoon, eating normal supper with his family. He repeated Tylenol 650 mg. around 6 p.m.. Over the last hour, he has developed noticeable swelling on the left side of his mouth ( lips to cheek). Tongue and throat seem normal. The only Benadryl that he had on hand was in pediatric form (liquid) so calculated dosage close to 50 mg.. How long will it take to work and what should he do?