About 4 days ago I thought I felt a spider on my back when I woke up. I had a look around but could’nt see anything so thought no more about it. The next day I noticed this red mark above my wrist. It looked like a bite initially because it had a center point to it. That has disappeared since and it’s now just very dry all over. I’ve marked the edges of it as I think it’s increasing in size. Co- incidentally I’ve been having arthritis type pain in my thumb joint above it but blood tests have come back negative for arthritis. My mother has psoriatic arthritis but again my c reactive inflammatory blood test came back. Any thoughts ? Thanks !