Chronic rectal itch

I have had chronic rectal itch for over 2 years. My gynecologist recently gave me Proctofoam HC, and recommended a rectal biopsy when I had my colonoscopy. The GI md refused to do the rectal biopsy, saying it should be done by a dermatologist because it is on the "outside". Why would my gyne give me Proctofoam if it is on the outside?  Anyway, do dermatologists do rectal biopsies, and could it be a chronic yeast infection? Fungal creams and other topicals have not helped. It is a horrible itch, similar to a vaginal yeast infection itch. Thank you.