You are most likely looking at a urinary tract infection. That will be treated with antibiotics and recovery should be quick. If at all possible, attempt to get a urine sample (a very hard thing to do), but the vet will ask if you managed to get one. If you do not think it is possible, my vet told me that if I confined a cat to a carrier for at least 2 hours before the vet visit that they would be able to locate the bladder with a needle and syringe and draw a urine sample. You may want to ask/try that.
Best of luck with Cubby.