Oh shit, Benson, quit it, please! Judy, you must be so worried. I’m so sorry!
Just from what you described about the day/car ride/vet, I wouldn’t be too worried about the bad poop. I’d have a bad one, too.
Did you go to a regular vet or a specialist (like a rehab/ortho type)? If I learned anything from MP, it is to just go straight to a doggone specialist after maybe one check in with the regular vet...if possible. Everything from diagnostic process to treatment plans are like a whole different world of tools. At least that was my experience. Another thing about x-rays is that it’s more of a crap shoot than you’d think, even if they're good ones! MP’s rads didn’t look as bad to a radiologist at the University as she was exhibiting, and reading those notes ("looks unremarkable considering the symptoms", my rehab vet noted that certain things just don’t show up as dramatically as one would assume, and that her shoulder rads *do* look pretty bad to her (so, in this case, a “general” radiologist is missing a lot of info that a rehab specialist w/specific familiarity of imaging could see). Anyway, so, they often said, “treat the dog; not the labs.” I also found that X-rays can vary quite a bit in quality, too: in a general environment, you’re concerned about everyone's stress levels, etc. (as they should be!!!)—and you do what you can, as quickly as you can. At the U, they just knock ‘em all out and get what they need, no matter what. (I think I’m rambling, but what I'm trying to say rather shittily is that there’s lots of variables to imaging—so when they "Don't see anything," it could be the capturing or the interpreting.

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I’m a little worried about chiro unless it is someone who is like a chiro jesus—at least with all these unknowns! Just am! :S I personally wouldn’t until you know more. Maybe see a chiro for an exam, w/o treatment?
Laser is pretty harmless unless it’s a hugely stressful event—then it’s just not worth it as a crapshoot treatment. (Crapshoot, as in, not really sure where to even treat, per se.) Class 4 is the type most places use, because it is super strong and deeply penetrating, and *fast*; but it can also seriously burn (it can get pretty hot—laser heat + friction) if they’re not moving the wand constantly, and you lose a lot of "beams" to scatter. Class 3 is the older technology, but it won’t burn and you keep the wand in place (= no loss to scatter). It takes about 2x (?) as long and doesn’t penetrate as deeply, but Benson is little and it was plenty strong for MP. And, with some patients like MP, it can definitely lower seizure threshold because of all the dilation. To minimize risk, my rehab vet manually dialed down the Class 4 settings to Class 3 level. It took longer, but was muuuuuuch safer. Depending on where you go, they have "less trained" personnel (just assistants; not techs) do the laser because the machines come with cookie-cutter programs that's determined by weight/coat/size/type of issue ("acute pain vs arthritis"). Pros and cons for that, since it's usually cheaper than a doctor or certified tech doing it, but then you don't have a doctor or tech doing it.
If it turns out to be a relatively straightforward soft tissue/muscle issue, you could try needle trigger point therapy—it’s like releasing spams via acupuncture needle. (It’s not acupuncture at all.) This does not feel good (it can be owie) but it is quick and can release the knot when nothing else can. MP had to have it done a few times.
I think acupuncture is pretty safe unless it’s horribly stressful for Ben. Some vets won’t do acupuncture and chiro on the same day. Too much for a lot of older, frailer fuzz.

I think it can be very helpful for improving general wellness, more than symptom specific stuff.
What is his regular pain tolerance? Is he usually pretty vocal/squeaky/obvious when something is even a little bit owie (i.e., is he usually stoic or a big fluffy baby?) Any other signs of pain? (Can't settle, panting, avoidance, etc.) Sometimes they just can’t move their bodies right for other reasons (e.g., neuro) and their gait wonkiness is not pain related.
I hear you about wanting to avoid drugs! If he is crazy inflamed, you may have to do something so that he can actually heal. Your doctor should be able to find a way around the kidney issue, whether by meds or icing or whatever. Galliprant is a newer drug that is marketed as a non-NSAID anti-inflammatory because it isn't your standard COX-inhibitor. I believe it's been most successful w/dogs that are just starting to be owie. I couldn't give it the time it needed to see if it would work with MP and ended up with Metacam towards the end.
If you can, try to get as many videos as you can to show vets you might see later. I’d put the camera down on ground level or about B’s eye-level, and let him walk through the field of view a few times. Have him walk towards the camera, and also get side views. Try a rise from a down, sit, etc. Easier said than done, I know!!!
This is bringing back some massive owie-related feelings and anxieties *and* I'm kinda short on time, so apologies for the unedited novel! I hope it makes sense.
Many hugs to you guys!!!