My son just went through chicken pox and it does sound like that is what your son has. I was told (by the nurse) not to bring him in because it's highly contagious and they wouldn't want other kids, especially infants and pregnant women catching it at the doctor's office.
We kept children's benadryl and oatmeal bath around in case he needed it. Keep him out of the sun. It lasts 7-14 days. Our 4yr old daughter did not catch it from him even though they were together the whole time he was sick. (we live in a small apartment so it's hard to keep them seperate.)
My son didn't itch and had around 30 bumps. He got an unusual headache about 3 days before the first bump appeared, other than that he had no fever and no other symptoms. It was a mild case that lasted about 6-7 days. Someone told me that if you catch it after vaccination then it normally isn't too bad of a case. Hopefully it is mild for your son too.