Kitten Peeing on Rugs and Furniture?

Just before Christmas 2019 my sister brought home a kitten from the vet's office who was going to be put to sleep because his owners didn't want him. I took him in and hadn't had any problems until the new year. He is approximately 19 weeks old.

About a month and a half ago I found a poo on our rug. The night before I had just wormed him and it was a syrup so I just put it down to stress because of the situation. He was using his litter tray perfectly before this and kept using it, but every few days there would be a poo on the rug. I tried pet carpet cleaner, but it didn't work so we just ended up rolling up the rug and putting it out of the way. Then he was using his littler again perfectly until he started peeing on our sofa. It go so bad that we had to throw the sofa away and I replaced it with a bean bag for the time being. I've just come home from work to find that he's peed on the bean bag now. I don't know what to do? Whatever I move or replace he pees on the next thing I put there. He has a good diet, he's wormed regularly, he's putting on weight consistently, he's had all his up to date on vaccinations, and generally he's a really well behaved kitten. Please if anyone has any advice I would be grateful.