I have endometriosis and presently on nuvaring from 6 mnths. I have 2 more weeks before my periods but have cramps and brown discharge. Pls advice?

OK. With endometriosis sometimes a therapy can work for a while and then not work as well. Often medicines need to be switched from time to time. Sometimes the uterus needs a break from a medicine and stopping treatment for 2 weeks then restarting will fix things. And sometimes there is another reason (polyp, fibroid, cyst, etc) for a new symptom. I would recommend an ultrasound first.
Worry not. You are likely trying to break through your NuvaRing and start a period, especially if you have been taking the NuvaRing continuously for endometriosis suppression. As long as the pain is controlled, it is ok.