Cat Peeing Everywhere

For the past week or so, my cat has been peeing just about everywhere in my apartment but his litter box.  He'll gladly poop in his litter box, but he won't pee.  The timing both correlates somewhat with me switching out to the World's Best Cat Litter, and also returning from a week-long vacation I took where I left my cat with my parents (who were also watching my sister's two Chihuahuas) in surroundings that's he's only in a few times a year.

He's peeing into clothes, on couches, in his bed, etc.  I have been able to confirm that he is still peeing at least a little bit as recently as a couple days ago, but I don't know if that's still the case.  For the most part, his behavior hasn't changed significantly.  For the first few days after we were back from vacation, he was a bit more irritable and meowing more, but that's mostly stopped, and he's been eating and acting normally otherwise.  I have a message into his vet to see what they recommend, but does this sound more like a behavioral thing or a possible UTI?  If it is behavioral, what else can I do?  I'm disabled (in a stamina sense), so it's getting very difficult and tedious for me to try to seek out all the spots he's leaving and to clean them up and I'm just tired and frustrated from everything smelling like urine.

You can confine him to a small space, like a bathroom, with litter boxes and washable things like towels and then you should get him to the vet asap to check to see if there is a urinary problem. 

He's probably spraying. At least that what it sounds like to me. Especially with him being more vocal than normal. Is he neutered? Even neutered cats will spray from time to time unfortunately. Usually on vertical surfaces. During your vacation did he come into contact with any female cats? Maybe ask your parents...that is if he isn't neutered. Other than that maybe it's a territorial thing from being around other male animals?

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He's been neutered for almost 7 years now.

I took him to the vet.  He appears to have a bladder infection, although his culture returned negative.  His pee was cloudy and bloody when they did a urinalysis.

They gave him an antibiotic shot which was supposed to work for 10-14 days, an anti-inflammatory, and 5 days worth of pain meds to help him along.  I've also started adding additional water to both his dry and wet food when I feed him.

It's been about a week now since the vet visit and while he did start using the litterbox to pee a few times now (he wasn't using it at all before), he is still peeing on the furniture as well, so I'm kind of at a loss of what to do.

Many cases of bladder problems are NOT an infection but crystals that irritate the bladder, and this is most frequently seen in cats that eat a dry food diet.  Since the vet gave him a longlasting antibiotic shot (which is most likely CONVENIA) yuo should put your cat n a probiotic because the Convenia kills most of the intestinal bacteria as well an a lot of cats have digestive problems after that.  There is one available at most pet stores by Nutri-Vet that I used on the cat I rescued who had been given Convenia twice in a row and it really helped.  I also got her off dry food entirely and switched to a diet of grain-free wet food with NO ADDITIVES (many pet foods have replaced grain with other additives that raise the carbohydrate level just like grain did).  A cat fed a wet food diet of mainly meat (not vegetable) protein, moderate fat, and low carbohydrates normally produces a slighlty acidic urine (pH 6.0 to 6.5), and that dissolves the most common kind of crystals.  Plants and carbohydrates produce a more alkaline urine and that can produce crystals which irritate the bladder like microscopic glass shards and can make them bleed.  The cat I saved was in severe distress when I got her, peeing bright red blood every 15 minutes and moaning and straining when she did it.  Two different vets had treated her with the antibiotic Convenia, but no one had changed her diet and she was still eating dry food.  It took three weeks of the new diet, extra fluid and pain medication before she was completely normal again, but she has been fine ever since on this diet with no medications, and it has been 16 months now, and prior to that she had been having urinary problems off and on for over a year.  Diet is very important when it comes to urinary problems, especially with males, who can block easily.