Yes, you should contact your doctor as chest pain can be heart related especially if discontinuation nitro causes chest pain.
"According to the American Heart Association, an ECG stress test’s reliability is only 67% which means that a stress test may in fact have a false negative or a false positive. There are a number of heart attack related instances that a treadmill stress test will not be able to identify. It will not, for instance, identify vulnerable plaques which is known to lead to heart attacks."
Your dotor has a responsibility to find and treat the underlying cause of your chest pain, etc. It seems to me your symptoms overrides the stress test results...could be a false negative, etc.
Thanks for sharing your experience, and if you have any further questions or comments you are welcome to respond. Lets us know what happens going forward. Take care