4yr old has fever 4 days after starting penicillin. has neck pain and fever that goes away after taking advil (ibuprofen). should we go back to the er?

Penicillin failure: With a child - why take a chance? The fact that FOUR days of penicillin hasn't done anything proves it is not effective. If it's a bacterial infection, there could be resistance. If it's viral or something else, the diagnosis is still in question since they gave u an antibiotic that doesn't work for that. You need answers, so pls go back. Tylenol/Motrin only affect temp not the disease itself.

Fever: Chances are, your child has a viral condition that is not responding to penicillin. if fever and neck pain persists a return to the ER for a recheck would be indicated

I would seek care: Given the residual fever and neck pain further evaluation is necessary. If you have a pediatrician or family physician I would contact them. Otherwise the Urgent care/ER is an option.