crease there is a red rash I have itched it a couple of times which has inflamed it. It does seem a little like a blister to some extent, but this could be caused by itching
itch? Or could it be Herpes? Or itch caused by public lice? Would anything like this come on this quickly? I am not a small man, and I sweat a lot. I am not used to much sport either. I have no girlfriend, but do not make a habit of sleeping around.
Since you say that you had protected intercourse, it is unlikely, though still possible to have some kind of STD.
There are many causes of groin rash, some of them being fungal infections, allergies, intertrigo, rash due to inner wear etc.,
In your case it seems that you have intertrigo or fungal infection, which is a irritation caused by rubbing of sweaty and warm body parts against each other.
The doctor can easily spot and treat this using local steroid/fungal application as well as oral treatments including anti-histamines.
Hope this helped. Let me know if you may need any more information.