I followed the same pattern of inflammation being discovered in the ileum just above the J Pouch many years after I got the J Pouch. I have an indeterminate diagnosis and whether it’s Crohn’s or pouchitis does not really matter. What matters is if it responds to treatment or not. Inflammation of the Ileum just above the J Pouch is actually quite common because of backsplash stool into the ileum (the J Pouch has no backsplash valve whereas your colon did) and also because people tend to get strictured at the J Pouch inlet. These factors create a backsplash and inflammation situation above the pouch and an indeterminate diagnosis.
I had success using long term rotating antibiotics (continuously) and, eventually, Remicade/Methotrexate to treat it and chronic inflammation in the J Pouch. Inflammation in the ileum can be more resistant to treatment and if so this could be further evidence of Crohn’s. Your treatment is probably headed in the same direction. You have to treat the inflammation or it will get worse. Good luck.
5 ASA is Pentasa and it’s unlikely to work alone but try it. It’s typically helpful in combination with antibiotics or biologics but as a stand-alone treatment it’s not likely to resolve the situation.