i had the itch, the dryness, and redness (cant say that it got darker) went to the doc, and they said i had "Jock Itch"
Treatment for that is 1st, is fungal, so it likes sweaty, dark, moist area
so you gotta make the opposite for that down there (cant help you with the darkness though, lol) just keep showering but pat that area dry, and keep it dry
worked for me in about 4-5 days
well i must admit that my situation that i explained is the closest to yours.. and i have not really experience it again. untill there was slight redness in between my leg and my inner thigh. but valsaline took care of that almost instanly (like in 2 nights).
Now i would have to say go to a doctor bout it. trying not to scare you but it sounds like you might have a "STD". i hope not though. and again, not to offend, you might wanna have your girl get checked out and ask if shes ok down there.