Help!!! FTM, What is this rash!?

My little man was diagnosed with RSV in early December. It was mild and required no hospitalization. He was even almost completely without symptoms by Christmas! Then, New Years Day, his cold like symptoms came back. A few days later, this rash appeared out of nowhere!

Does anyone know what this could be? He has an appointment in 2 days with the pediatrician and I’m trying to avoid the ER during the flu season. He hasn’t tried any new foods, we use baby laundry detergent, and we haven’t tried anything new as far as lotions/soaps. Please help!