Belly rash

So my son has been sick (already been to doctor and er) and he had a rash on his stomach that the doctors say is just from the fever and aren't too concerned. It does seem to fade and come back, but he hasn't hit a fever since yesterday morning and even then it was a low 100. We're still waiting for cultures and blood work to come back (sometime today) so I will be back in his office later today. I guess I just want reassurance that it isn't nothing more. He's 3 months old.