What Causes Light Spotting Followed By Severe Pain?

Hello my name is rakshita, and i got married last month i had mated last month and i had taken a i pill after 24 hours. My periods regularly use to start on 25th of every month infact i had bleeding for one day but the blood was in black colour and suddenly bleeding stoped from the night and i am having a sevoir pain:please let me know is there any chance of pregnency.Regards Rakshita