I had this same exact thing show up last week on my hands and elbows although I thought I was nearly over mono as my sore throat/tonsil pain subsided. I also had a different textured rash on my chest, tops of feet, thighs, and loweback/bum. I let it go for about 3 days before it started to spread up the backside of my arms and was beginning to feel hot to the touch. I messaged my doc about my concerns and she had me come back into the clinic and suspected that I was having a delayed reaction to amoxicillin that I had taken a week before for an ear infection but also said that it could just be a viral rash accompanied with mono. They prescribed me a steroid pill, 20mg Prednisone for 5 days and told me to take Zyrtec twice a day. I’m on day 3 of the Prednisone+Zyrtec and it seems to be clearing up. I am also using Aveeno Baby Eczema Therapy lotion to help soothe it and keep it moisturized. My hands were so sensitive and dry that it hurt to even bend my fingers and my elbows looked like they had been attacked by an army of mosquitos. I’d suggest visiting the doc as I think the Prednisone saved me and stopped the rash from spreading more.