Plonkers Vet bills

I normally wouldnt ask for help for this but I have a male cat(Plonker) that plonked himself on us a few years ago after maybe being abandoned by his previous owners or sought us as his future forever home. Over this time it became apparent that he has "baggage" from his former experiences and is a very delicate emotionally. He started showing signs of urinary problems with the vets to this day are still working out the cause. He currently is on "cat prozac" and anti-inflammatories. The other night after an emergency visit hes now on yet another trial medication. My funds are limited as I look after my mum full time and I really dont want to euthanize him as he has an amazing personality when he isnt struggling to pee or in pain. The vets wont extend any further credit to me which means Im having to consider that option. This is my last resort to try give him the help he needs.