At this point, the chances of being pregnant after a vasectomy are really low - less than one percent. If your husband has already had the recommended amount of tests to clear him and he had the OK to begin having sex again, then the reason for your late period is likely not pregnancy, but probably has more to do with weaning your daughter as breastfeeding and stopping breastfeeding can affect your cycle.
I would wait until you’re at least a week late. At that point, go ahead and take a test just for peace of mind. If the test is negative and your cycle is still MIA after two weeks, call your doctor and just let them know what’s going on.