What Causes Bleeding After A Week Of Menstruation?

i got off my period about 4 or 5 days ago which was about 7 days long. I don't even have a regular monthly, it's like the last day every day with just brown blood instead of red blood because i have had mirena for about 3 1/2 yrs now. tonight i went to go pee and the toilet was full of blood but yet no blood on my underwear. what is going on here? is it stress or something more serious?