Can someone taking nortriptyline for fibromyalgia also take tylenol (acetaminophen) w/ codeine?

Yes, but. The rule of thumb is always caution with combining sedating meds. Combining medications, any medications, presents problems with drug-drug interactions. Sedating medications such as t#3 with nortriptyline will be greater than the sum of the parts. I see you also take methacarbamol, which is sedating as well. Caution is advised. Also look at the amount of Acetaminophen in your excedrin. Caution.