I understand what you mean by stinging being a relief from itching. I wonder if acupuncture has that effect- ones nerves focus on the needle prick with acupuncture and the itch is not the focus of the brain. I so get how lack of sleep will drive us insane- I would lay in my sleepless bed and plan ways to kill myself- yet that was not with GD, believe it or not the itch, sting and burning skin was worse for me with my Allergic Contact Dermatitis before I got diagnosed after having the 5 Day Extended Patch Test. Avoidance of allergens is key to controlling those rashes and sensations and surprisingly have had dramatically fantastic results giving up processed sugar and limiting natural sugar.
When I looked up MGUS it did state that it can mutate into lymphoma and also that rash could be one of the side effects. Good news you tested benign to lymphoma which is truly a concern. There was no description of the rash. Heck you could have GD along with rash effects from the MGUS.
I never tested positive to GD with biopsy, but my symptoms are classic and I do have it. Yet if you tested negative to lymphoma in 2014 you clearly didn't have it then or you would be symptomatic by now, more than just enlarged lymph nodes. Lymphoma was a big fear for me, it's a tough one. It's good you still have your blood tested, I used to have it done semi-annually but now just annually just in case the leukemia returns.
We both need to seize the day because we are surviving and our skin right now is a good as it ever will be!!!!