There are often litter box problems with cats. This is not an uncommon occurrance. It is the largest contributor to problems people have with cats. There are other places on this website that deal with several of the causes and what to do to help your cat.
However, I have not yet dealt with one of the main reasons a cat will have problems, and that is because it is not behavioral. Not really. Feline Urinary Tract Diseases cause as much of a problem as anything, but since I'm not a veterinarian, I can't really help much. I can advise you to see a vet - that's all. And that's pretty much where we start if your cat is having a problem, anyway.
Your lovely furball, suddenly starts avoiding the litter box. Maybe she is going all over the house and you can't figure out what's going on. Maybe she is trying not to go at all... That means she is in pain. Get her to the vet. Male cats have a lot of trouble with a condition called "sands" where there are uric crystals that develop. It's like kidney stones, and very painful. All cats need to be seen immediately if they have any changes to litter habits. This is very unlike a cat!
During and after treatment, the cat may associate the litter box with the pain. This can drive your cat to find another place to go. Move the litter box to a new location until the cat is better and using the box correctly again. Deodorize the misses and try not to punish or scold your cat. It's really a very natural response - avoid pain. Your cat wants to be fastidious and clean. Your cat wants to not be in pain. Your cat wants to feel like her old self again. This will happen, but not overnight.
You should follow the vet's advice for changes in diet and litter box filler. Watch to be sure the medicine got the infection and that your cat does not get sick again. After three years of kedney and bladder infections myself, I can tell you that the pain is very real, and the infections are debilitating. The medicine may fix one thing and cause other problems. So just be kind to kitty. She needs your love.
