Welcome to Pet Talk Jellicoe. I'm so sorry to hear that your cat Belang is so sick. I would take him back to the vet or another vet and try to get liquid antibiotics or antibiotic shots as was suggested earlier. He may also need a different kind of antibiotic or a larger dose. When my cats have had URI's I have usually noticed improvement within 3 days after giving them their meds. Good luck and please keep us updated.