Vet update: today we went to see Jude's regular vet who diagnosed and has treated Jude's FD as well as the various issues including the UT problems he's suffered these past couple of years. A different vet performed his dental on Friday, and then we saw yet another vet when Jude's fever spiked to 105 on Saturday, so I was glad to get a consult/examination from someone who knows Jude well.
The vet doesn't think Jude had an infection at all, and is taking Jude off the doxy and does not want him to take the Onsior that the vet prescribed on Saturday. He thinks that Jude's fever spiking on Saturday was a reaction to the specific type of anesthesia ("old-school" was the word he used) the dental-vet used on Friday (Jude's vet worked in the same practice as the dental-vet, so he knows exactly what they use in their procedures). As an aside, he also told me this: the x-rays I paid extra for when they performed the dental are pretty much worthless as they don't have an actual x-ray machine in their clinic, but rather a digital x-ray machine which doesn't capture a picture of the roots of certain teeth

. But, I digress.
Also, I've suspected that the doxy, which has a flavoring in it, contains sugar and is responsible for spiking Jude's bg numbers. I brought the bottle with me to the clinic, and Jude's doctor smelled it and agreed that it smells like it has alcohol in it (sugar), so I'm hoping that by discontinuing it his numbers will start coming back down. You can see on his chart that his numbers started going up on Saturday night, after the first dose of doxy. We'll see if that is the culprit.
The vet also checked Jude's mouth today for the "serious case of stomatitis" the dental vet told me Jude was suffering from. He showed me Jude's mouth, and he pointed to a small--tiny, really--reddened area and said that's the stomatitis--it's very small. He said that level of stomatitis ("mild") should not be causing Jude any problems, but he recommended a toothpaste to use (the one I mentioned a while back that I've already purchased), and we will keep an eye on it. One thing he mentioned to me about the toothpaste is this: he said that since it's enzymatic, it's not necessary to brush the teeth, just to get the toothpaste on the surface of the teeth (
@MinnerPip). He said using a gauze wipe would do the job.
Fingers and paws crossed my little guy can soon get back to his normal self.