2 day period??

Ashley
I started my period a day earlier than expected and odd symptoms that came along with it that I don't usually have (very tender nipples, gassy bloating type cramps, etc).... But it only lasted 2 1/2 days and was very light.. before AF I was getting brown discharge as well. My periods are usually very regular at about 5/6 days.
I don't think I'm preganant because two days before expected period I took a test and got a BFN. I'm just wondering how common this is for you ladies? Is there a cause? I've never had this happen and I have not been more stressed than normal