Please explore low dose naltrexone for pets. Vets would give you a prescription. It is prepared in a compounding pharmacy. I used to order it from overseas, for myself. There's a post here on EC about LDN.
You can use red light therapy as well. My cat loves it. I wish I could post a photo.
Lastly, acupuncture, to stimulate healing mechanisms.Yes, acupuncture. When I have severe back pain an acupuncturist treats me at home (I pay extra). One time I had mentioned my cat did not pass stool or pee for several days, she put few needles into my cat at no charge The cat urinated in an hour and the next day passed her stool. I was impressed. She, the cat, was also not eating, and started eating the same day.
LDN, red light and acupuncture stimulate body's healing mechanisms so it heals itself, whatever is broken. You body as well as your pet's body knows what is wrong and how to heal it