My cat keeps peeing on clothes I leave on my couch! Help!

My almost year old cat has started peeing on my clothes but only when i leave them on a couch. This started when one time I forgot to clean the litter box and she had nowhere to pee, but ever since I make sure to clean the box every three days so she has no excuse. I try to keep away my clothes but yesterday I forgot and left an expensive jacket on the couch and obviously she went for it! Please, I need help!

By cleaning the litter box, do you mean that you're only scooping out the poop and pee every 3 days? I would say if you have one litter box for your cat, you should be scooping it once or twice a day. You might consider getting a second litter box also to help her have more places to relieve herself when the box in full. Usually the litter box recommendation is 1 box for each cat plus 1.

Sometimes cats just like to pee on clothes, and keeping it away from them is the only way to stop it. But since this is a localized issue, in addition to keeping clothes off the couch I would also get an enzyme cleaner to destroy the smell of urine on the couch and clothes. Other non-enzyme cleaners won't be able to break down the urine smell, so you cat will continue to smell it and remark the area. Natures Miracle is available in most pet stores and a lot of people have luck with it.

Is you cat spayed? An unspayed cat will spay much more than a spayed on.

Definitely clean the box at least once a day.  If you think about it, would you want to go in a toilet that hadn't been flushed in three days?

Keep the clothes up.  Get Command hooks for the coats, and everything else put straight in the hamper.  I have a cat that nails any item of clothes left out, and the only way to stop it is to not give the opportunity.

The most effective way of preventing your cat peeing on clothes that you leave on your couch is not to leave them on there in the first place.....

And following that:  

You need to clean your couch to rid it of the enticing cat-toilet smell she has made, as recommended above.

You need to scoop her poo as soon as you notice it and scoop her pee at least once a day if you use clumping cat litter.  Consider changing to non-clumping litter so you'd only have to keep an eye out for poo.

Change the brand of litter.  She might not like the one you're using.

Use two litter bowls - some cats, especially females (in my experience), like to poo in one bowl and pee in another.

Vet check her for a urinary tract infection.

Spay her.

Have you moved the position of the couch, her litter bowl, food bowls, any other piece of furniture, or made any other changes to your home?  

Has something new been put next to her litter bowl?  Can she exit her litter bowl freely & easily in more than one direction?  Does the position of her bowl give her privacy to pee?

Is there someone new coming into your home?  

Are there any smelly socks or shoes lying around?

If I were you, I would take her to the vet and check for a bladder infection.  When my cat had a bladder infection, she peed in odd places, intermittently, including the bathtub.