I had asked for some further information and have not heard back.
It is appropriate to be concerned about the possibility of liver disease.
For the vast majority of people, this would not be an emergency. The only times that this would be an emergency would be if there were more severe symptoms, particularly severe vomiting or abdominal pain.
If there are no severe symptoms, then this can be evaluated as an out-patient. The first step, if not already done, would be to check blood tests of liver function, along with other screening blood tests, such as electrolytes, kidney function tests, and a thyroid
If there are no severe symptoms, then it would be fine to wait to get these tests done once your doctor's office opens.
Your doctor can also discuss tapering off the nortriptyline, which would usually be done over several weeks, and also should occur in the context of a discussion of using an alternative for the migraines.
If I can provide any clarification, please let me know.