Have you engaged in fisting or been with a hooker lately? That could explain volumes.
A number of years ago, I had what seems to be the very same symptoms as was described. After seeing many doctors (and I mean many) who repeatedly thought that my condition was the average jock itch type problem, I had the oaccasion of meeting a Doctor at the University of Miami.
After hearing my history of doctor visits without any relief, He immediately diagnosed it as an irritation to clothing dyes, and recommended that I henceforth wear only loose fitting 100% white cotton underwear (white boxers). In addition, he said that I should wash my underwear in dye free & perfume free detergent (All Clear is what I now use). Further, I make sure that the clothes go through the rinse cycle twice as an added protection.
He said that this condition is not nearly as common as jock itch, but is more common among soldiers who are on active duty. During my other Doctor visists, and due to my problem not being the typical jock itch, the medications that were prescribed actually made it worse for me. I started getting some relief after 3-5 days of just wearing 100% white cotton loose fitting underwear, along with washing the area and keeping it clear (with a dye free and perfume free white soap - I use Dove for this).
It sounds like some form of irritation. It does not sound like ma fungus. I agree with your plan to see another dermatologist, although the treatments given by the first one seem reasonable enough. I would suggest paying little attention to thew redness, as apart from pain, because irritated rashes in the groin can look deep red long after they are gone, only to fade eventually on their own.
Best.
Dr. Rockoff