Jerry, this has to do some what with allergies, e.g. Calvin takes Wal-Finate twice a day, and I keep 5MG Prednisone tabs on hand. Given only when he really needs it (I keep a log when I give him one. So far during the spring and early fall rainy seasons. He takes one tab per week). He also takes a 10MG tab of Metoclopramide to help him move his food though his digestive system.
I tried a few brands of limited ingredient type of foods, settling with Royal Canin's limited ingredient. Hill's Hypo-Allergenic biscuits, and kept him on Harlee's Pedigree Jumbones (I started her on this treat when her pancreas flared up).
I take Calvin in every 6 months to do his semi-annual blood work to keep track on how he's doing (although 5MG Prednisone is a low dose), as well as for my peace of mind!
One thing that's great about his DOC in Phoenix is she has a blood annalist machine in her office!
Since you live in one place, e.g. don't move around like I do. May be do an allergy type of test.
Anyways good luck!
Pops