If you were my patient, I would advise you that the morning after pill is fairly effective if taken before ovulation and within 48 hours of intercourse. Since you don't know whether or not you would have ovulated on this cycle yet, it is difficult to give you a number as far as effectiveness goes. Also, if you regularly take birth control pills, I would advise you to continue with them. If you are not already taking them, I would probably not start at this point, as then things could become very confusing. I WOULD recommend that you use a back up method of birth control if you are not using pills.
Hope this helps!