hi Scooby,
My DD daycare has also had a bout of chicken pox.She had a pock on her foot and my GP said 1 pock dosnt make chicken pox and she has had the vaccine. My DS has also had them but I didnt get them then and have never had them so Im guessing I may have an Immunity of sorts. My GP is also my OB and explained that there are some people who are immune to things while others seem to contract everything. If your really concerned talk to your FS. This should put you at ease.
I know they check for measles, mumps, rubella just incase you need a booster. Im not sure though if they do this during PG. Oh and HIV is another.
Im sure if you didnt get them when your son got them you should be fine but again talk to your doc.