Can you get bed sores from your wallet?

Ok so about a month of so ago I noticed a pain in my butt check under my wallet when I would sit down. I didn't think much of it, until it after 4 weeks the pain was still there and when I began to investigate I noticed that I had a series of little bumps in the area, approximately the size of a pencil eraser. They are a deep blackish purple. Are these bed sores? or Pressure sores? And what can I do to fix this? And why has this happened only on the side where my wallet is and not the side where I keep my Copenhagen?