Period or implantation bleeding?

I was supposed to start my period on the 12th of this month. I started bleeding/spotting on the 11th. My period is usually really heavy. I usually have to wear a pad and a tampon. I have only been wearing pads for these 4 days. Everytime I would check there was little to no bleeding. I kept expecting the bleeding to get heavier, but it never did. I am on my 4th day of light spotting with slight cramps. Could I be pregnant?