It didn't agree with me - I was on 10mg and it made me incredibly tired - I needed to sleep 12 hours a night or so to feel human.
My IBS is much better managed now than it was. This is a combination of significantly reducing my stress levels and changing my diet.
I bought "the low fodmap diet" on Amazon and it had lists of all the different foods in the front - I was able to spot one list in particular that made me really quite unwell, and having cut them out completely (I explain it as being like lactose intolerance), I am much better than I was.
I hope the amitriptyline does agree with you though.
Meds wise, I found a combination of mebeverine (for stomach cramps), omeprazole (excess acid) and simethicone/"windeze" (for trapped wind) was the best combo, topped up with loperamide if I was having real trouble with diarrhea/moderate trouble and had a long car journey or whatever.
I don't find buscopan as good as mebeverine - I just take it on top if the others don't work.
With the diet and lifestyle changes above I have got to the point now where I don't take medication regularly any more and it is a lot easier. I feel lucky I have got to this point and it does take careful management.