My kids had them before the vaccine was even available. Not sure if you have any more kids in the house other than your 6 year old but if you do, ask your doctor about getting Zovirax for the others. My pediatrician told me several years ago when she diagnosed my older one with them that it would only be a matter of time (15-21 day incubation period) before my youngest would come down with them. She said second cases in the house are usually (not always) worse than the first case and she would prescribe the Zovirax at the onset of the second child's chicken pox. Sure enough, two weeks later, Taylor came down with them - got Zovirax started within 24 hours and his outbreak was not bad at all.
You've been given some wonderful advice on treating his symptoms (no cure, it has to run it's course). Use the Aveeno Oatmeal baths to help with the itching and give benadryl too (I'm sure your doctor told you about that). Main thing is to do what you can to help prevent him scratching them. Don't let him get too hot as that makes the itching worse - keep him cool. Oh, and lots and lots of ice cream and popsicles
Best of luck to you and your little one!