text: This is kind of funny but I answered the same question for my female friend less then two days ago because she had the same issue, same problem! I researched it for her as a medic that likes to study gyn and here's your answer: The surge of hormones in your body causes your endometrium (lining of the uterus) to become extremely thick and then fissure and crack (so to speak) at your fourth week and then to fold and flush out of your body(menses). When you take the pill it enforces a state of pregnancy on the body and causes your endometrium to thicken and stay thickened so that you cannot become pregnant because your body already thinks that it is. So when your on it for three days or more esp. right after your period your endometrium starts to thicken again rapidly due to the surge of hormones the pill is providing, but then you suddenly come off and your body is like what the hec!?! I need to flush my lining again but it's not thick enough for a complete mense so it just releases the little that it's built up by infrequent spotting till the lining goes back to ex nhilo, or the beginning of a fresh cycle. So it's really nothing to worry about at all unless you starting cramping terribly and have spotting into the two week range. Then you should see your gyno. I hope I covered everything if I missed something post an additional detail and I'll do my best to answer it.