Two Light periods in a row?

So I keep track of my period on my cell phone with an app, Last month I was on time but It was a very short period, I am not on the pill, and usually my periods last a 5 to 6 days and this one lasted maybe 3....than this month came around and I was a week early and I had a lot of old blood for a couple of days...but it was spotting, a little bit here and there. Than I started and lasted all of two days. The first day was heavy and than the next day it was really light and than the day after it was gone...I'm not sure whats going on and I was wondering if anyone else had experienced that?