What Causes Delayed Periods?

Hi..last month I had met a accident...after that my period has stopped..I was worried..and after pregnency test it was negetive..then one day my husband eject inside ..next day I took meprate 10grm (3days)..to clear my period..but its 8days over..nothing happend..am I pregnent?is it possible to consive in a day..my last period day is 13th december..is this medicine affect my baby??plz help me...l have polisistic overy also