Sobe update:
Had urine tested again yesterday - MUCH improved. Protein has gone from +2 to +1, bacteria infection drastically reduced, concentration improved. Due to their still being some bacteria, they have sent the sample off for a culture and he had another shot of antibiotics last night, as it seems to be working (albeit slowly).
The vet weighed him and he's gained 300 grams in just over 2 weeks!!!!!! That's half of his weight loss. The vet and I are soo sooo happy. Woohoo!
We may need to add in a second antibiotic to fully clear the UTI but he's definitely feeling better. We are refilling the food bowl all the time and loving it!!