Help!

I am on BC . I had unprotected sex on my break week about 3 weeks ago & he never came at all. Well, I am on my 3rd month of BC , and I started bleeding a week before my period was supposed to begin. I don't think it's implantation because it has been going on for almost a week , plus I have had severe cramping and i dont know how I would be pregnant at all. I just need other opinions . The blood has gotten heavier since day 1 of bleeding but now that it's almost over , it is getting lighter . I am using pads that I change like 3 times a day . Do you think this could be implantation or an irregular period ?