Hmmm period or what

Okay so I had my period at the beginning of this month and it was a pretty typical one. 7 days, heavy bleeding, fat blood clots, miserable, the works. But I started another one two days ago and it's already over... It was also a week early. So two in a month? That's weird for me. That's actually never happened. Could it have been implantation bleeding? How does implantation bleeding and period bleeding differ?