Don't have it, but I did a little research for you. One thing for sure... you are not alone!
Before I give you some links, let me give what little advice (not necessarily informed) that I got from what I read:
1) Stop using most of the creams, lotions or ointments that you have tried. They can make the problem worse.
2) Definitely change detergents AND throw away every pair of undershorts you have and buy new ones. Buy a week's worth of jockey types AND a week's worth of "tightie whities." Reason? The loose ones may help if you need "air." But, sometimes it is better to put close fitting cotton "between" areas of skin that otherwise would touch each other and spread or worsen the irritation. Stay with one or the other type for a week or two exclusively to see which works best.
3) Look at your diet... especially snacks (like peanuts)... and try changing it dramatically. Whatever you eat MOST for snacks... eliminate it totally for a few weeks.
4) Try to remember what (if anything) you started, stopped or changed dramatically about the time you first noticed the problem. This could be food, soap, detergent, cologne, etc. [even wife or girlfriend!] If no change in partner... ask HER to think about the same things SHE may have changed about that time.
Okay... I'm out of medical advice. Now... read this first link and then read all the pages (5) in the discussion:
Help for Red Scrotum Syndrome - Men's Health Message Board - HealthBoards
Notice at the bottom of the page(s) that there are several other threads about the same topic on this messageboard. You might want to check them out, too.
Here is the google search link I used, and you may find other info there that will help. I didn't check the Wiki links, because I don't really trust them.
red bag syndrome - Google Search
(if that link doesn't work... just google red bag syndrome)
I checked out "neurodermatitis" but I don't think that is what you have. I also checked on yeast infections with the same conclusion.
After you stop all other creams and stuff that you listed... and against my own best judgement... to ease the discomfort and what I assume is alot of "scratching" that will only make things worse, try the "roll on" version of Cortizone-10 with aloe. Apply it and let it DRY before putting on your undies. This MAY give you enough relief to give other remedies time to make a difference.
Best of luck, and I hope I was of some help.