What Causes Severe Pain And A Brown Discharge In Menstruation?

I'M 19 and i'm on nuvaring for about 3 months now to help me with the severe pain i always present when i have my menstruation. This month has being very weird because for about 2 and 1/2 weeks i been having brown discharge and some times brown pieces. I want to know if this is something serious or if it is normal. Should i go to see my doctor?