Hello Good Evening, This might be either implantation bleeding or regular period or pill side effect bleeding: Implantation bleeding – a very early sign of pregnancy – occurs when the fertilized egg attaches to the uterine lining. During implantation, the fertilized egg (called a blastocyst at this stage of development) burrows and embeds itself underneath the wall of the womb (uterus). Because the uterine lining is rich with blood, some women can experience spotting and even cramping during this process. For the most part, implantation bleeding is lighter and occurs earlier than your regular menstrual period. Sometimes, however, implantation bleeding may be heavier, so it can be easily confused with a regular period. Emergency contraceptive pill side effects may include: tubal pregnancy, nausea, diarrhea, or stomach pain, dizziness, tired feeling, breast pain or tenderness, changes in your menstrual periods; or headache. So all the possibilities are there, so you should wait for next 5-7 days and get urine pregnancy test done, but in my opinion very few chances of your pregnancy, so be relaxed this time. Regards, Dr. Naresh Jain.