Hi, the bleeding could be due to either your menses or the side effect of the postinor 2. Postinor 2 is not an ideal method of family planning and it can cause abnormal vaginal bleeding, My advice is that you please get a proper method of family planning. Also it could be your menses and so watch it and let me know how long it lasts.. To exclude implantation bleeding, do a pregnancy test 2 weeks after the sex and it will be negative if you are not pregnant. My advice, till you know the actual cause of the bleeding is not pregnancy, use condoms and do a PT(blood) once it is 2 weeks after the intercourse. Subsequently go for a proper modern method of family planning.
Thank you and kind regards.