If the man had a post operative sperm count, and it was zero, then if you are pregnant, its not by him.
You might not be pregnant at all. Take a test. If it is negative, test again in another week. If still negative and you are still thinking you are pregnant, see your doctor.
i heard sometimes the vasectomy can all of a sudden get reversed? thats what i heard ... like peek said give it another week or two then test or see your doctor. also ur period could be late due to stress or anything else.