Implantation Bleeding

I have been bleeding for the past week. The first two days were light pink spotting or nothing at all. Days 3 & 4 were heavy enough to fill up regular tampons and I had to wear a pad overnight. Days 5, 6 & 7 have been lighter but I've still worn tampons but they haven't been totally filled. Now that it's towards the end it's darker brown blood/discharge. Is it implantation bleeding or AF?