period or preg?

I've taken 3 pregnancy tests, they've all been negative. However my period came 5 days early. The first two period days were heavy as usual, the Third was lighter than usual. I noticed spotting today which is period day 4 for me. I suspected it could be implantation bleeding, but I read that that normally happens a few DAYS after sex, in my case it's been 2 weeks since we did. Help???