Does Light Menstrual Bleeding After Having Unprotected Sex Indicate Pregnancy?

Hello, I m 24 year-old female and had unprotected sex 2 days ago, where he pulled out before ejaculating. (This is NOT my normal form of contraceptive, and alcohol was involved) My period is due in 7 days but this afternoon I had light bleeding (which has never happened to me before), and I m wondering if it was possible that the bleeding was due to implantation. I can t remember when I ovulated, but I don t think it was anytime in the past week due to my cervical mucus (I ve been doing some research to relive stress). I m planning on grabbing the Plan B One Step pill during lunch tomorrow and a few pregnancy tests. I just want to know if it s possible that I m pregnant. Thank you.