First, since Nosey's signs involve his whole right side and he has loss of sensation, this isn't likely related to a pinched nerve. These tend to only affect a single limb and often are painful. Furthermore, if he had had circling and is stepping in his bowl, I would be most concerned about a brain based issue. Now toxicity and diffuse infections (ie Toxoplasma --and likely why he was started on clindamycin) are a concern; but if his signs are all on his right side, then we'd also have to be wary of a lesion on the left side of his brain (since limb control is via the side of the brain opposite). In regards ***** ***** we can see these signs with sudden bleeds in the brain, soft tissue inflammation, cysts, focal infections (abscesses) or tumors.
Now it sounds like your vet has been thorough and we'd hope those toxicity results are clear. If they aren't, then they will guide treatment. Otherwise, we'd have to consider further diagnostic imaging. Specifically, in situations where brain based issues are suspect, MRI would be the test of choice as it will allow your vet to see the brain itself and what changes are present. At the same time, we often will take spinal fluid via a spinal tap to diagnose those infections concerns.
Overall, your vet's tests and treatments thus far have been reasonable. But if he isn't responding to treatment, then we'd be concerned of these additional differentials and need to consider MRI if toxicity is ruled out.
Best wishes for Nosey,