There are a few things it could be:
IPS (irritable pouch syndrome)- similar to IBS, a functional bowel disorder. Treatment is the same: diet, antispasmodics and low dose antidepressants.
Small Bowel Bacterial Overgrowth- treated the same as prouchitis, with antibiotics and probiotics for maintenance. There just is no evidence of pouch inflammation.
Nerve damage or trauma: the nerves in the area of pain were traumatized by surgery or became entrapped in scar tissue, and never recovered. After a year or so, if it has not improved, the damage is considere permanent. Treatment is pain medications, nerve targeted medications (like Neurontin or Lyrica), opiates, antispasmodics. Nerve blocks can also be done.
Reverting to an ileostomy may or may not help.
Jan