I just found out the edicine prescribed for my stomache pain is actually and antidepressant.?

I have had some really bad pain the in my stomach forr a couple years. within the last year it has gotten worse. numerous tests. Tests showed thickened walls of gallbladder, and fatty liver. My doctor is not concerned about either. Im pretty sure this is whats causing my pain. Anyway long story short. He, the doctor had prescribed some pills for me of which he said were for pain. well I took them for a month and when I went back he prescribed me three more months worth .They didnt help and I dont want to take them anymore. When i first filled the prescription I didn"t read the paper that comes with it. i just took the doctors word. This last friday I wanted to know exactly what I was taking and it is call Nortriptyline. It is an anti-depressant. That freaked me out. As i already take Paxil and I am trying to get off it. I dodon'tant to be on another one. I am upset because My doctor did not inform me of what exactly I was taking. I dowon'tee how an antidepressant has anything to do with ststomachssues. This doctor is a gagasteroenterologistwhy would he prprescribehis for me. I have since stopped taking it. dumped it all out. somebody enlighten me.