It is contagious for two weeks AFTER coughing starts, so I'd still be concerned and take daily ascorbic acid rather than just once.
It's probably that it won't be a big deal in you, but because you are pregnant there is already a lot of compression on the lungs from the baby growing. So I'd be concerned about the number 1 side effect, which is pneumonia. Hernia, incontinence and weight loss are also side effects that may occur and be not good with a pregnancy. So keep a close eye on any complications and fever as well, which can be bad for growing babies.
Big hugs mama...it is much more probably he had allergies, this is the worst ragweed season in years.