There is no supplement that will help this condition. Most supplements are a waste of money and not all are benign as you noted above.
It will say on the bottle something like:
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure or prevent any disease.
In my opinion you would be better off spending your money on more testing.
So, go back to the vet asap. The first thing you need is a diagnosis. The band aid treatments didn’t work.
He may need an ultrasound and whatever else the vet thinks in necessary to get to the bottom of this and start an effective treatment.
Best of luck
PS: In the meantime, a soft diet (only) may help.
