What Causes Prolonged Bleeding?

I am 40 years old and up until now have had a regular menstrual cycle lasting 28-30 days with a normal period lasting 4-5 days. About 2 weeks into my last cycle I began bleeding. More than spotting but less than my normal period. This bleeding has consistently continued for 4 weeks now. In the last week or so the bleeding has increased. How do I make it stop? What is the cause? Do I need to be concerned? Is it perimenopause?