One period stops, a week later another one starts????

I am so confused I was on my period, pretty normal, for a week, from Sunday to Sunday. But now here I am a week later Exactly, Sunday, and I am on my period again. I have heard of periods starting and stopping within a week but for one to last a week and then a week later come back bigger and better than ever?? Not to mention I have been having some pregnancy symptoms, which make no sense if I am having so many periods! Someone shed some light on this situation. The same exact thing is happening to my sister and we have both been having out of whack periods for like 2 months. What is the deal??