WHYYYYY

So I missed my period last month, but it came this month and is really heavy. I usually have a 5 day period and usually on the fifth day only a little blood comes down cause its finishing up. But on this period it so far has lasted 6 days and is still extremely heavy so I fear it will last way more than six days. I am on no type of birth control or medication. So has anyone experienced anything like this before. Or does anyone kno what this is all about