About 16 days ago I had a 2 day period that came earlier than was expected. It was pretty heavy the first day and extremely dark blood. The second day was very light and mostly brown/pink blood. I thought I might be pregnant so I took a test and it was negative. Now, 16 days after that, I'm starting again. Mostly dark blood again and pretty heavy, more like a normal period for me this time. Normally my periods are about 26 days apart though. And that first "period" I had was not at all normal for me. What would cause this and anyone else had an experience like this?