There's really no way we can tell you what's going on over the Web. There are so many things that could be causing the symptoms you describe. It could be allergies, but it could just as easily be something completely different.
Your best bet is to contact your son's doctor to make an appointment or to take him in the local urgent care clinic to be evaluated. So please do that, won't you?
Hi there, took my son to the hospital, the rash was getting worse. they kept him in overnight. They said that was an allergy to anything, he had been playing outside all day in the garden, plus i had brought a new towel and just wrap him in it.
Please do not take any chances with this. Please take your son to a doctor as red bumps can be a variety of different things from very minor and minimal to serious. No way to tell without visual evaluation.