white spot on penis head

I have had this white spot (~1.5mm in diameter) on my penis head for months..and it has had some raised red-rash around it which is now subsiding but not totally gone.  Have gone to the Dr. about it but they can't figure out what it might be.  They said red rash may just be psoriasis, but the white spot is what concerns me.  The white spot is flat and has not raised or grown into anything at all...such as a blister.

FYI..I did the HSV1/2 tests two times (4 months apart to make sure).  Any ideas?