Why don't you ring the Health Direct helpline. They can advise whether you need to be concerned and take your DS to the docs or not. They are registered nurses on call 24/7 and are national so doesn't matter where you are. Their number (in case you don't have it) is 1800 022 222. Its probably just the virus but asking the question of a professional won't hurt. I know when my DS who is a little bit younger than yours have random spots on his body they put it down to virus.

HTH