Burning, uncomfortable rash on bottom

[jedidad]

About a month and a half ago, I began a chiropractic program for a back issue.  I was sent home with an exercise program that involved sitting on a "wobble" ball and performing movements that will strengthen my low back.  The ball is basically a round rubber pillow that's aired up.  A few times when I have done these exercises, I noticed it was causing some friction between my buttocks.  Eventually this became a rash around my anus and surrounding area.  After talking with my chiropractor, he suggested doing the exercises without the wobble ball until the rash went away.  

I don't feel the discomfort when performing the exercise anymore but I can't get rid of this rash.  I sit in an office chair all day at work and I think it's complicated the healing process.  I started with hyrdocortisone which kind of helped but not when I had to sit for a while.  So then I started using my son's diaper cream.  The rash does not itch at all.  It burns and is only relieved when I can get up to walk around.  The diaper cream has worked around my anus but the rash seems to have migrated to the area between my scrotum and anus.  I've been medicating that area but perhaps the way I'm sitting has caused further issues.  Now I have the same kind of rash (almost like a rug burn) on both butt cheeks just outside of the anus area where the rash began.

So it would seem like a heat rash, I suppose, but not sure how to treat it.  I wear boxers so I thought maybe the bunching up of material was causing problems and switched to "whitey tighties," but this has not helped.

Would something like baby powder work better or some other product?

Thanks!