Emma,
 
I will answer your question, but I must give you some of my background before I do because my "feeling better" is probably not going to be the same as yours.  When I started treatment three years ago, I had had IC symptoms for over ten years.  I had been taking Elmiron and Atarax all of those years and was doing pretty well.  Even before full-blown IC symptoms started, I had signs that it was coming, but I ignored them because I had no idea what was coming.
 
As far as what led to my full-blown IC symptoms, I have always had a weakness of stress affecting my bladder, even since I was little.  And I was mis-diagnosed with mitro valve prolapse in my 20's and was given 12-18 antibiotic pills to take all in one day everytime I went to the dentist (this was a common practice at that time, but it is no longer) so that I wouldn't get a fatal infection in my heart through bacteria travelling from the mouth to my heart.  I was also given antibiotics because of the mitro valve prolapse during labor and delivery of my three children.  In all these cases, I was given antibiotics without having any infection present!  When my IC symptoms started, I was given several rounds of antibiotics because the doctors thought I had a stubborn bladder infection.  To top it all off, I had another ultrasound done to see if I actually had mitro valve prolapse, and I don't.
 
So you see, I have a long history of prescription drug use.  If I knew then what I know now, I obviously would have made different decisions.  I just trusted that my doctors knew best.
 
So fast forward in this timeline to one year before I started treatment.  In the summer of 2010, I started experiencing intense vaginal itching and burning.  I went to see my gyno, and he said I probably had a bacterial infection because there was no yeast that he could see.  He did not send a sample to a lab to test it, but he sent me home with antibiotics.  This only made things worse because it wasn't a bacterial infection, it was full-blown vulvodynia.  (I had had mild vulvodynia even before IC symptoms started, but once again, no doctors ever clued in on what might be going on.)  So my gyno gave me estrogen cream and other stuff that didn't help, and then my IC symptoms started getting so much worse.  The Elmiron and Atarax were ineffective at this point.  So I went to see my urologist, and he gave me a bunch of meds to take to get the pain under control, and one of those was Elavil.
 
So when I started treatment with Dr. M, I was on six different medications.  Within nine months of starting treatment, I weaned off of all of them.  I just wanted them out of my body, come what may.  My body went into a tailspin, and it took about 18 months before I had some consistent, more functional days.  But even now, my body needs a ton more unraveling of all of this.  I haven't been able to get past List 1 with food, and I don't wear jeans, and I can't drive myself anywhere because I end up in more pain.  I have not had any pain-free days for four years.  
 
BUT I have gone from constant intense bladder and vaginal pain to having level 3 pain for weeks at a time.  I have gone from having absolutely no sex of any kind to being able to do certain things with my husband (but not intercourse yet).  I have gone from ONLY being able to make my own meals to being able to function more around my house.  I have gone from only being able to lay down and stand up to being able to sit for hours and be relatively comfortable.
 
For me, the above is "feeling better," and I know it will continue to get better even though it is a long road for me.  Emma, you have only had IC for two years (Though two years is too long!  I'm not discounting your pain.)  So I really think that your body will recover much faster after going through the initial painful period of getting off of Elavil.  Alternatively, maybe if you slow the process down even more, you may not have to experience much pain at all.  Even while I was on Elavil, I still had pain, and I know you said you are basically pain-free on it.  It is a powerful drug, even in small amounts.  I never took more than 25 mg at a time.  But because of our imbalances, we are sensitive, and small amounts are all it takes to alter our body chemistry significantly.
 
I hope this helps.  I know it is long-winded, but I needed to give you an explanation because I am one of those complicated cases.  You will get through the transition and to the other side and all will be well.  It's just not an easy process.  But it will happen.