If you could bring a urine sample to your veterinarian and have it checked they could tell you if your cat has diabetes and/or an infection. If they won't look at it without an appointment you could buy some urine glucose dipsticks. You would need to get a clean urine sample without litter in it and compare the color change on the stick to determine if there is sugar present. We sell the urine sticks. If you order it from us you might also want to order some Dia-IonX which is helpful for the symptoms you describe. Generally it is also beneficial to give probiotics and Omega 3,6,9.
Please let us know what you find out and we can help you with other things that would be good for you to know.