What Causes Abnormal Vaginal Bleeding With Stomach Cramps?

I finished my period 8 days ago( normal) am on BC and use pull out method, but stated cramping and bleeding tonight.... Had sex 2 nights ago.... Could this be another period starting so soon? I also have two cysts on my left ovary. ( showed on U/S last month) i also have endometriosis, could a cyst have ruptured and caused the bleeding and cramping?