Straight after your period, your fertility is normally very low but what most people forget is that woman have 2 ovaries - normally only one ovulates at a time but in many cases, they both can ovulate - hence non identical twins. So basically, you can never be sure. But if you took the morning after pill when you were meant to, then you should be fine - try not to worry and if you period does not come when it should, take a pregnancy test as soon as possible.
