Do try and remember everything you're using from soaps and conditioners to detergents and lubes.
When I was a kid the people who make Tide changed something in it and I developed an allergy to it. Since then, I've had to use hypoallergenic detergents with no dyes/perfumes. It's kinder to my boys and the clothes.
I'd also suggest using a very gentle body wash rather than soap. MSNBC held a physician panel where they looked for the best skin products on the market and they found
these products were superior. You may want to try those. The Dove body wash is wonderful stuff.
Gold Bond medicated powder is good for after showers but make sure you're completely dry down there before you apply it. Use a handheld hair dryer on low/no heat and be sure to get in all the crevices. Refrain from shaving your pubes if you do that. Shaving's very irritating even under the best of circumstances.
Good luck with this! Itchy nads are awful.