If the cat has a UTI that is an infection and there is nothing to do but take him or her to the vet to get treatment for it. If it is a UTI, it requires antibiotics in order for the cat to get better. There is simply no legal way to obtain those without going to a vet.
If your cat does have a UTI please get him or her to the vet as soon as possible. The cat is in a great deal of discomfort, and will not get better without a vet. Furthermore, it's likely the cat will begin having inappropriate urination issues without treatment.
It's a vet visit and bottle of antibiotics $75. if you wait until the cat is really sick it will cost you thousands to get her out of trouble or lose her altogether. A UTI is very painful as well.