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.
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.