I have now been on birth control for four months. I have taken them everyday, at the same time of day, no skipping, whatsoever due to me being overly paranoid. Three days ago, I started my period pills, thus my period started then. The night before I started my period pills/period, I had unprotected sex. This evening, my period stopped. Earlier today, I had also had some heavy exercise while working in the back yard. Could the exercise be what stopped it, or could I be pregnant?