Off birth control...

Got off bc the 6th.. Had a pretty heavy bleeding a few days after like a normal period. Stopped last Thursday. Today had light cramping and some bleeding. Not much. And it was really red at the beginning and now a darker red with some brown... We've had sex several times before the period started etc.. And after. Could this be implantation bleeding or am I out of my mind? Surely it could happen that fast could it??