What Do Rashes On The Body Indicate?

My grandson visited a week in Louisville, ky. In October, 2017. His symptoms were hands, feet buttox, legs, tummy n face had spots, rash looking. He had been on antibiotics 2 or 3 weeks earlier with congestion, high fever runny nose. He had been traveling from marshal islands, army base to Oahu, hi. For a week before he came to ky. I took him to a dr here n at first he thought hand n mouth disease. But due to prior antibiotics being his first time on them, it was determined that it may be a reaction. So no treatment was given just a diagnosis. It went away after 5 days. The army moved them to Madison, Alabama now. Been there since February 1. He woke up yesterday with these symptoms again...what can it be?