Morning After Pill: Understanding Spotting & Effectiveness

Question
hi,
Last wednesday afternoon (sep 14th) i took the morning after pill, and the second one that night (my last period  started the tuesday before, sep 6th)  Today, 5 days later, I'm experiencing some light spotting.  Does this mean that the pill has worked?  I do not know much about the pill, does it work by causing the endometrium to shed thus preventing implantation?

Answer
If your last period started on September 6, you would not have ovulated before September 19 and could only have become pregnant if you had sex on September 18,19,20, or 21. You could not have conceived if you had sex on September 14 and did not need the morning after pills. The bleeding you had today sounds like it was due to taking the pills. The morning after pill helps prevent implantation. I doubt that you became pregnant. However, if you do not get your period around October 3, wait an additional week and take a pregnancy test. Don't worry.