Bit of a late answer but I have been on them both.
I take stemetil as needed for menieres disease (inner ear condition) and have taken amitriptyline for chronic pain relief for arthritis and tummy problems. A number of doctors from gastro, rhumatology, GP etc... to pharmacists have been well aware I am on both and had them on repeat prescriptions together.
It took a long time for me to be diagnosed with my tummy problems, they have now found bile acid malabsorption and say they may well find inflammation indicating something like Crohns at some point and have a further scan due.
It was the best part of 20 years from first ending up in hospital due to tummy problems to getting a diagnosis and some help and I think a lot of conditions like IBS can be difficult to treat and have so many potential factors affecting them such as diet and stress.