My cat started peeing outside the litter box and I don't know why. Everything changed overnight.

Three weeks is actually a meaningful timeframe. When a cat who has been perfectly reliable for years starts eliminating outside the box, and the vet has already ruled out a medical cause, the next question I always ask is: what changed in the environment around the same time? Not necessarily something dramatic like a move or a new animal. It can be something much quieter, a change in your schedule, a new smell in the house, a noise outside that started recurring, even a shift in where you put the box. Cats register these things before we do.

The fact that he chose the bathroom mat and the couch is also information. Soft surfaces are a common preference for cats who have developed an aversion to the litter itself, either the texture or the feel underfoot. Before changing anything else, I would try offering a second box with a completely different litter type, unscented and fine-grained if you are currently using something else, and place it near where he has been going. Not as a permanent solution but as a diagnostic step.

Feeling defeated after three weeks of this is completely understandable. If you want to work through the specifics together, the assessment I do through the Work With Me page is designed exactly for this kind of situation. You fill in the details about your cat, your home, and what happened, and that structured process often surfaces the detail that changes everything.