Hi chiiaki;
Sorry to hear about your issues with your cat. I was in a similar situation years ago with IBD and I switch to an integrative vet due to the fact that I wanted to go to a species appropriate diet. I think if I was in your shoes I would be doing the same. Our conventional vets were not taught species appropriate diets in college or university. So if you can find a vet who has stepped outside the box and learned about homeopathy and natural path he you will end up having the best of both worlds.
When it comes to constipation an integrative vet will be able to suggest other alternatives for treating that problem which would be easier on the cat.
When it comes to urinary tract issues I have found that switching to a species appropriate diet, and homeopathic remedies would alleviate the problem. The major issue I have found is the pH factor of the urine. If it is up around 7 pH then you start having issues. A raw food diet usually puts the pH down around 6 1/4 to 6 1/2 which alleviates a lot of issues. Kibbles are noted for causing urinary tract issues
I think I would be checking the Internet to see if there is a holistic vets in your area, and then making some phone calls to see if they specialize in treating cats with your issues before making an appointment.
Please keep us informed, and we would sure like to see a photo of your cat.
Here's a website you might find interesting it covers a lot of your issues, raw feeding, urinary tract issues, antibiotics, and constipation.
https://catinfo.org/making-cat-food/