This happened to me with my last pregnancy.
There is only an issue once your son shows spots.
Call your doc/midwife to check your immunity. They say that 99% of people are immune, that even if they don't think that they had the chickenpox that they were exposed and have the antibodies.
I happen to NOT have the antibodies, so if either of my children develop spots, I am to go to the hospital within 96 hours to get a shot. My doc explained to me that the risks are very low..but the concerns are serious enough... hope that helps.