Strange period?

So I just had a period that was a week early, heavier than usual and lasted 16 days. I had my hormones checked. They came back normal. Not pregnant. This has never happened to me. I'm 32 and have had very regular periods and they became pretty painless after I had my children. Usually they only last about 4-5 days with maybe a day or two of heavy bleeding. I'm planning on seeing my OB this week, but I'm just wondering if any of you have ever experienced this? And if it was just a one off or something else?