see another vet before your kitty becomes fully blocked.
I can't imagine my vet just sending my cat home when they could barely urinate. My vet wouldn't release mine until they were urinating well without a catheter....Royal Canin Urinary S/O...I swear by it.....available from vets or petsmart with a prescription...works for cats with ureteritis as well as stones...sometimes it is hard to detect what the blockage is....whether it is stones or just irritation...
Bring your cat to another Vet...she can be blocked.....seriously i see that often, more in male cats but it can happen to females too.
If your cat has crystals in her urine, you need to keep the ash content in her food as low as possible, because high ash content can cause a cat that is prone to forming crystals to form more of them, and this can lead to urinary tract blockages. It's a lot more common for male cats to block up than females, but it's not unheard of for a female to develop a blockage. Try to find food with an ash content of 3% or less. Avoid all fish products, because with fish cat food, they grind up the whole fish, bones and all, and this adds a lot to the ash content. They make foods now specifically for urinary tract health. Nine Lives makes one and a couple of others. One of my boys had a blockage almost a year ago, and I've been feeding the urinary tract food since then for all of them, and it is working just fine. The link that Savas provided contains some excellent information for you.
Ghilly
Well, it depends on if there's an infection. Did he do blood work? It sounds like a stone/s (just guessing here, if so, could need special treatment)...regardless unless instructed otherwise hydration is important to kitty. generally a cat gets 80% of it's liquid from food, so a good wet food is key as well.
I'm going to provide a link here on kitty nutrition. It would be a good thing to know a bit more on the subject for you so you can avoid this sort of problem coming up again. It discusses what are some good foods, and which brands/types don't really cover the needs of kitty, which are more complicated than they let on.
http://maxshouse.com/feline_nutrition.htm