My 3.5 Yr Old Grandson Went To Urgent Care On

My 3.5 yr old grandson went to urgent care on Tuesday with a high fever, body aches, runny nose, chills. After about an hour tylenol took effect, seemed fine there. Tested neg for flu swab/strep throat. Told to keep him on tylenol, he should be ok in a few days. As of today, when tylenol wears off he seems droopy and sleepy. Complains of leg aches, and seems worse, late afternoon, really sweaty-cool bath, kept complaining of head and legs hurting. Had accute asthma as an infant. My daughter had been consulted about a possible cyst during her preganancy, and was told if baby made it to term, could possibly take care of itself. Any relation?longest he has gone withohut tylenol is approx 3 hours