Constipated, and UTI -- Need advice.

I have a .. Male white Persian, and he's already had a prepubic urethostomy about two years ago for crystal blockages and small urethra. He's been on C/D dry and wet, and drinks plenty of water. He has a vet appointment for tomorrow (Wednesday) at 9, and I talked to the vet who (as I've stated in another post) told me to get a urine sample and he'll just need a shot and some antibiotics. He's a very nice vet.
This is my baby, he's about 10 years old going on 11. He's still very active. I've noticed he's also a little constipated, so I tried giving him canned pumpkin. He'd have none of it. But, he's still very playful, purring constantly, eating both dry and wet and drinking. I'm trying not to worry my head off but I am struggling not to follow him around constantly. Any advice on how to calm down, since I'm more stressed about having to take him back to the very place that took his.. *ahem* thing, and caused him so much stress before than anything else. He's not running a fever, isn't droopy, ... I'm just so worried about him. Is there anything I need to try to do until the appointment tomorrow morning for him? I've read about some people force-feeding a small amount of pumpkin for constipation, but I'm afraid to do that. Any help is appreciated. He has lots of names, but we mostly call him Boo-Boo.

Since he doesn't like the pumpkin, you might try a conventional hairball treatment, like Petromalt or Laxatone. They act as a mild laxative--and they are flavored, usually like malt or fish. Some cats will eat them on their own, but for those that don't, you can smear some on their front paw, and most will lick it off.

My Vet told me Coco can not have Pumpkin because of her Bladder Infections. For some reason she sugested hairball stuff for constiption. ever since she got old she gets Constipated. Watch your Cat for a Uti because sometimes you think its Conctipation and its a infection again.

Thank you guys so much. Yes, I keep a very close eye on him, and when we go in tomorrow (they already have the urine sample, and it was plenty!) I will tell him about the constipation. He is still purring and playing, eating and drinking though. I just pray they won't find anything else, and he can get his antibiotics and get outta there Thanks you guys.