If you just have an itch bit don't have a visible rash, you probably don't have a fungus. You may well just have irritation, which is common in this area. My suggestion is to keep the skin moist with any lotion you like, and to apply an itching preparation containing menthol, camphor, or diphenhydramine (available without prescription--ask your druggist.) If these fail in a week, please ask a doctor to have a look.
I have had the condition exactly as described, and it was the common fungus called "jock itch" (Tinea cruris). If you already know all about jock itch, ignore the rest; if not -- read on.
Probably every young man has a mysterious first encounter with this reddish itchy condition that burns when you scratch it. Each of us must be educated about this. A normal cause would be wearing sweaty underwear for too long, which provides good conditions for the fungus to grow. The solutions are to bathe down there twice daily, drying thoroughly, then apply one of the products from the drug store (non-prescription), such as Tinactin, Lotrimin, etc. These come in ointment, powder, and spray forms. Getting out of gym or sports clothes promptly after exercise, showering, then getting into clean, dry underwear -- is important, even though it is sometimes not convenient to do.
With all due respect, I would give these steps a try before going to a doctor. And be forewarned if you have never had "athlete's foot" that the same symptoms will happen to your feet from wearing sweaty socks too long, especially if you are exposed to the fungus (Tinea pedis) by walking in a public shower. Hope some of this is helpful.