Dog has begun peeing in crate overnight-puzzled, suggestions welcomed!

I adopted a Chihuahua/terrier mix in June, approx. 18 months of age. It took a good 2-months to get the potty training right & at 5 months he began to let us know he needs to go out. In all that time he never messed in his crate. He is let out at 9pm before crating for the night. We take his water bowl away around 630pm. For the past 3.5 weeks he been peeing in his crate. I took him to the vet & they checked his urine, which was fine but gave him a round of antibiotics just to be sure. The antibiotics were finished a week ago and no change. The vet said if the abx didn't help it was probably stress. Nothing has changed in our household so that doesn't make sense. The only change made was to his food. I asked the vet if food could be a cause and she said probably not. 12/26 I switched his food to Acana. He seemed itchier than usual so on 1/2 I switched him to Zignature. That is when the peeing in the crate began. 1/9 is when I took him to the vet and abx were started and the next day I switched his food back to Fromm that he's been on since owning him. I tried crating him at night without his usual three blankets thinking he wouldn't pee because there'd be nothing to absorb the pee in his crate. I put a sweater on him last night to help keep him warm and woke up to find dried pee on the crate floor and his sweater damp with pee. I've read to take away water bowl hours before bed, take away blankets in crate and make sure he is tired at bed time, none of that is working. It seems as though he is not so bothered by peeing in his crate. I'm puzzled. This may warrant another vet visit to see if other medical issues could be the cause. Any suggestions/advice would be most welcomed!

We don't put ours i a crate. We did get one when we intended to fly but we didn't and it never got used. We gave it to a friend.

In the two years we have had our dog he has peed in the house a couple of times.
This worked:

It could still be a Uti, one of my previous dogs kept testing clear until they did an in depth test and it came back as e coli and took three rounds of antibiotics to clear it.
Although you say there have been no changes, you've changed the food 3 times, taken his bedding away etc.
I honestly can't see what taking his bedding away achieves, yeah it cuts down on washing but removes his comfort, what's that supposed to achieve?
Why do you believe he's not bothered by peeing in his crate, if he has no option, can't go out what choice does he have if he needs to go?
You could try getting up in the early hours to let him out, maybe pin down roughly what time he's going.
I'd do that, let him out every couple of hours and see what happens, if he wasn't house trained when he arrived he could just be reverting to type, so treat him like a puppy and start from scratch again, failing that go back to the vet

Chihuahuas have tiny bladders and it could be that a last wee at 9pm makes the night just too long for him to manage. As the owner of a bitch with spay incontinence, I understand your frustration, but it seems that you have two courses of action. The first is to set your alarm for a wee break (or even two if he has a long stretch in the crate) during the night. If you are a light sleeper, moving the crate into your bedroom could help, as you are more likely to hear him becoming disturbed if he needs to go. If he is getting stressed about being in the crate, where he knows he has no option but to wet himself, he may be more relaxed knowing that you are close by.
Option two is managing the situation. You give him a bed consisting of several layers of newspaper, and top this a piece of Vetbed - which is designed to let water pass through whilst remaining snug and dry enough to sleep on. (I did not suggest a puppy pad base, as I have been told that they are treated with chemicals which encourage dogs to wee on them).
I would like to add that I am not a fan of routinely removing drinking water at 6.30pm. If the reason for the incontinence was to turn out to be due a UTI or an endocrine problem, withholding water could cause dehydration and damage the kidneys.

You could try a belly band with an incontinence pad if all else fails, that way his bedding stays dry and the wee is contained within the incontinence pad. If it's scent marking it will fail as the wee only reaches the pad and nothing else. This was how I cured a scent marker,he could pee to his hearts content but couldn't mark anything so gave up trying. Ours came from Glendarcy.

PS.
Trouble's comment has made me think. Are you sure that your boy is emptying his bladder before he goes to bed? A bitch will squat and usually pass the majority of her urine at one go, but a lot of excitable young males like to pass urine in squirts, so may need more than one attempt before they are sufficiently drained.

Thanks for the advice. Here's a bit more info. We never withheld his water before bed until this started. We've had him almost 8 months on this schedule and he's never peed in his crate even in the beginning. We were advised to take away his blankets and have a bare crate because his pee would be absorbed into the blankets making it not so unpleasant to be in rather than if he was in a bare crate laying next to a puddle of pee. It has worked for others. I assumed that when I found him the other morning with pee all over his sweater that it must not bother him too much if he couldn't hold his bladder I would think he would have left a puddle in a corner and avoided it. Hard to say. Sure wish the little guy could talk to me. And oddly enough, he did not pee in his crate overnight last night. Fingers crossed for more dry mornings.