I've A 3 Year Old Child , He's 16 Kgs

I've a 3 year old child , he's 16 kgs , n he has been for 8 days now with herpetic stomatitis n he had fever n ulcers n the Dr prescribed Zovirax and antipyretic ,, today he's severly ill again n he's having 40 fever n he has been coughing for 2-3 days now , is this a superimposed bacterial infection , shall I give him an antibiotic ??