My dad had a stent in his bile duct between the pancreas and the liver. His stent did not work well for him either, he had it changed 3 times, he would have massive pains in his back and stomach but once it was changed, he was 1000x better. Sometime the stent is not the correct one, his original one had an infection, his 2nd one was too short and the third one was longer and worked. It is definitely not normal for it to be changed so many times, but we encountered the same experience and were very angry. If this is where your loved ones stent is check his billiruben count so you know if the stent is not working, that shows up on the blood tests and have his checked every time he or she gets blood work.