Stopped using nuvaring and was still having regular cycles. Now 3 months later period stopped. Negative urine pregnancy test. Is this common?

Very common. Irregular periods are one of the most common problems obgyns treat. If this is one time problem it usually resolves on its own. If this is a recurring problem you should be evaluated. If there is a concern for pregnancy then do a home pregnancy test . There are many options available to help regulate the menstrual cycle. Restarting NuvaRing would correct the problem.