What Causes Granuloma Annulare?

I have a rash on my arms, thighs, stomach. Does not hurt, appears not to be contagious and does not itch. It is red, circular, almost like a ringworm, and has multiple small skin-colored bumps. Dr. did a biopsy and said it is Granuloma Annulare. In trying to figure out what is causing it, I have noticed that every area I have it is where skin touches skin, mostly in the way that I sleep. Could this be the cause of it?