My SD just got the rash last week and I freaked out after consulting Dr. Google (I really need to give that up). I spoke with my doctor, who said the same thing as the PP, its really only dangerous to a fetus in the 1st trimester. And most adults are immune to it because they either had it or were exposed to it sometime as a child/adult. Not everyone presents symptoms when they catch it.
I would try to be calm and wait for your blood results. More likely than not you're immune (I would be surprised if you haven't been exposed as a nurse). Stressing about it isn't good for your LO. That being said, I freaked the f' out...so I get where you're coming from. I'm thinking good thoughts.