rash on trunk

My 5 year old son has developed a fine, raised rash on his trunk.  It does not itch. No fever.  What could it be?  It is Friday.  Should we try to see a doctor over the weekend?

Although I'm not sure these things are related, he also had sharp stomach cramps one night and day about a week ago.  He also seemed a little tired.  A few days before that, he had mild cold symptoms.  

Fifth Disease is going around his school, but he doesn't have the pink cheeks or any of the other symptoms, except the rash currently and mild cold about a week ago.

Thanks for any help you can give.