There can be other causes of bloody urine besides a bacterial infection. Was the urine ever sent out for culture and sensitivity testing? It's actually quite rare for young cats to have a true UTI, more often it's
inflammation, not infection. Can you ask the vet for a copy of the urinalysis?
What does your kitty eat? Diet plays a huge role in feline urinary tract issues:
http://www.catinfo.org/?link=urinarytracthealth