Rash all over for 8 days now

My 7 yr old grandson woke up with a rash Sun 02/11.  It started on his upper back and chest, progressed down his torso, then down his arms & legs.  I thought it was Chicken Pox, even tho he had the vaccine in '04.  Mon 02/12, took him to his ped. who said "not chicken pox", its a virus or allergic reaction, give him antihistamine Diphenhydramine 25 mg 3 x day.  This had no affect on the rash.  

He was on the Methylphenidate patch for ADHD, with moderate site reaction of bright red mark under patch which lasted for 7-10 days.  Quit using the patch  as of 02/11.  His psych. said call when rash is gone, but don't put patch back on until I check with her.

I started giving him antihistamine Chlorpheniramine maleate, 2 mg 4 x day on Sat. 02/17.  The rash looks like it is going away on his upper back and chest.  I wonder if the antihistamine is working or the rash has "run its cycle".

It is all over his body, small conical bumps, a million of them.  They get a hard, white, hair-like protrusion, then turn "freckle" brown and flatten out somewhat. It is mildly itchy.  There is no blister that erupts, oozes or crusts over.

Any ideas?