Is it implantation ?

Hannah
So for the last two weeks I've had unprotected sex I'm still 2 weeks from my period and I did miss a few pills I'm on BC. Today I woke up with cramping and I'm lightly bleeding but it's a very dark brown. It's there when I wipe and barely much on the pad. Is this break through bleeding because of the missed pills or could it be inplantation? Any thoughts?