Problems with the urinary tract in cats can cause excessive urine production or an urge to urinate frequently.
If your cat has cystitis often the first sign you will notice is that it is passing small amounts of urine very often. Sometimes you will see blood in the urine and occasionally your cat will strain as if trying to go to the toilet but nothing comes out. In these cases cystitis may be mistaken for constipation or an obstruction in the urinary tract. A blockage in the urinary tract is more common in male cats than females. Obstruction to the urinary tract is an emergency situation so if you think your cat is straining to pee then you should contact your vet immediately.
Cats may also choose not to use a litter tray and spray or urinate in other parts of the house. This may be due to a medical problem but in many cases can be a behavioural response to stressful situations. In multicat households cats may avoid using a litter tray frequented by other cats and most cats will avoid a dirty tray.
If you think there may be something wrong with your cat's toileting habits then you should make an appointment to see your vet. Try to collect a fresh urine sample and take this with you when you take your cat to the vet. Your vet will be able to get a lot of information on what may be wrong with your pet from testing the urine sample.