What Is The Difference Between Implantation Bleeding And Menstruation?

hi I've been expericing light bleeding 4 days before my expected period is due , and I had unprotected sex a week ago . . . . I'm not sure if it's implantation or if it's my period . Usually my periods are on time and I don't experience cramps , on the first day of this bleeding I was having mild cramps around my pelvic area . And the color of blood fluctuates it doesn't really come out on the pad but it's red when I wipe and when I use the bathroom blackish blood comes out . I wouldn't say it's heavy or light