I also get skin sensitivity / abnormal sensations from tirz. I got it when increasing doses originally, and now I am on both tirz and reta, it gets obviously worse with tiny dose increases of either reta or tirz.
It is also weirdly patchy, often worse on my left shoulder, or both arms and occasionally it hits local leg nerves, thankfully it is pretty mild unless I accidentally have a slightly higher dose.
I have tried to research this and really cannot find much on it other than being mentioned as a side effect in some of the studies. It is interesting that it seems to be more likely from reta, and it was rare in the semaglutide studies, but in the high dose semaglutide studies of 7.2 and 16 mg, it was very common , up to 20%. So given that sema does not affect anything other than GLP-1, it more or less has to be a GLP-1 effect, which totally fails to explain why it seems to be more common with reta. I have discussed this with chatgpt , it does not seem to think there are any concerns about actual long term nerve damage occurring from it, and as far as I know there are no reports of nerve damage from GLP drugs, which is reassuring I guess.
There is no obvious pharmacology explanation for why you suddenly got much more severe side effects. Apart from some of them being made worse by having a virus at the same time. All you can really do is avoid dosing until the effects have settled down a lot, and restart a fair bit lower, and half the dose twice as often will make it easier to adjust doses up and down if needed.