why's my cat suddenly peeing...?

all over couch? a quick backstory, almost two weeks ago he was treated for a blocked urethra and crystallized urine. the vet said he might leak for a few days so not to be too alarmed. when the leaking DIDN'T stop (he's been leaking on my bed a couple of times a day) she put him on a medicine to help tighten his muscles so that he'd have better bladder control. well, we resorted to locking him out of the bedroom the last day or so and he started peeing on the couch. not leaking, he actually peed on the couch, right in front of me. he's still using the litter box too, so why's he doing this and how do we get him to stop?

Sounds like the cat is still in a lot of pain. When cats are in pain and they have to pee, they pee where they are sitting at the time, be it the floor, the carpet, the bed or the couch. He may need extra time to recover. In the meantime, keep him isolated with a clean litter box nearby.

Call your vet and tell your vet what's going on.A cat who pees outside the litter pan right in front of you is trying to tell you in the only way he can, that somethings wrong. It may be that the medicine to tighten the cat's muscles is causing painful bladder spasms and an adjustment in medication or dosage may be needed. I would recommend you get a large dog size varikennel type plastic dog crate and keep your cat in it with his litter pan, food, and water, while he's convalescing. This will confine his mess, make it much easier to clean up after him, and you also will be able to easily see how much he's urinating and if he urinates outside the litter pan, you will be able to see whether there's blood in his urine or not. Temporary incontinence and leakage after a cat has had a blocked urethra is a common side effect of the bladder being full and distended for so long. It usually resolves in time.