How Can Rashes And Blisters Be Treated?

I am a 45yr male, 188,6-0. excellent health..no issues whatsoever until now. On the right side of butt cheek..have a rash. I noticed it was like pimples/blister like..doesn't itch, burn etc. What could it be? How should I treat it?..I shave my scrotum and shaved my anus hair on a whim..bumps occured after that.