puppy hasn't gone potty in 18 hours!?

Is the temperature really cold outside? We've got really cold wind chills out and the second my dog feels the wind, he tries to turn and go back inside, even first thing in the morning when its been all night since he peed. Once its been more than 5 or 6 hours since he went, we keep him outside until he goes. Fortunately, he has picked up that this will happen and when he turns to go back in and we hold him out, he runs down the sidewalk and pees quickly and then sprints back in.

If it is cold out, bundle up and bring treats. Try running around a little as that can trigger a dog to go.

Last thing to consider, make sure she hasn't found a corner somewhere to pee when you weren't looking. We went out to get my dog to pee before bed and were outside walking for 35 minutes with no peeing. We gave up and came in figuring we would try again in 15 minutes and found that he had snuck into our room and peed on the bed (of all things right before bedtime) which is why he didn't have to go.

At this point, it might be better to let her out of the crate even if she does have an accident. Holding for 18 hours can't be healthy.

No it's not healthy BUT my Whippet went for 22 hours when we were away overnight. I took her out roughly every couple of hours (Reception thought I was mad!!) but nothing. In the end, we crated her and went to sleep. Next morning she went, by around 11 am in a motorway carpark. Clearly she got to the point she HAD to empty. I was honestly thinking I'd need to find a vet to catheterise her. Bitches can be difficult - to this day (she's 6 now) she has still not gone off her property, thankfully outside, apart from twice. The second time was another overnight stay away and that time she went from 9 am when we left, to around 9 pm.

I would add I have never used a crate to housetrain. Yes, as crates were initially intended, use one to keep her safe, out of mischief, but not for housetraining. That's best done by taking a puppy out every hour during the waking day when just 8 weeks, extending as she gets older. If you leave a dog crated, that may well mean they don't get to learn about holding, knowing you won't leave them crated for ages so they have no alternative but to empty in there.

This isn't your problem of course, but fact is if, by 5 months, this is going on, and she's not got the message that she empties outside, when you take her out and use the word you prefer, to produce the result you want, then you need to go back to 'puppy one'. Knowing when she must need to go. And if she's held for 18 hours, I think you need to see a vet. She's young for this, but it is possible she has a big bladder stone which has blocked her up. Bitches are less likely to do this than males who have a bone in their penis which will block up with bladder stones. Bitches usually pass all but the biggest of stones.

This is out and out abuse, cruelty and neglect! You don't leave it in a crate for 18 hours. Please re-home this dog with someone who knows how to care for a pup properly and never get another pet. I wish I could lock you in a crate for 18 hours! The crate should only be used when you can't supervise. Are you even feeding this pup? You may well be causing medical problems by what you're doing.