weird discharge ????? is this implantation bleeding ??

i’ve been having blackish brown discharge for the last three days .. the last time i had sex was three days ago , i am on birth control and have never taken a pill late . my boyfriend didn’t come inside of me . my period ended about a week ago , and i still have about two weeks until my next period is due . is this implantation bleeding ? ive been told that it’s just old blood but i’m not used to spotting when it’s not during my period .