Viral hives or allergic reaction ?

My 17 months old was sick since 4 5 days. He had fever cough and congestion. We went to doc she said viral infection and ear infection and prescribed amoxicillin. After that his daycare informed us that one of kid had rsv so we are assuming my son had same. He is taking amoxicillin since last two days. He is better do fever since yesterday. But today suddenly he had these rashes on his cheek out of blue. It was not itchy (He was drinking milk which he does everyday) . What can it be. It is fading but why he got rash suddenly? Can rsv virus cause these type of rash? Or was it amoxicillin which he took in the morning? Or allergic reaction?