What Causes Brown And Black Vaginal Discharge?

I'm 47 years old - had not had a period from Apri 2010 to Oct 2010. Since then have had constant vaginal discharge to the point where I don't really know where my regular cycle is on the calendar. Up till April I was a normal flow every 27 days for 3-5 days. Now it's constant - with browny-black liquid discharge that is very smelly. Haven't yet been to a doctor...is this fairly normal for premenopauseal women ?