Vaginal itching is unfortunately a fairly common condition. I would recommend seeing your primary care doctor
or your ob/gyn as, while it is most likely a minor condition there are a few serious conditions that could and should be ruled out.
The first consideration is if this is a skin problem. Skin conditions can be with or without rashes. These include a dermatitis from an allergic reaction as your friend suggests. Another common cause would be dry skin. The most worrisome concern is if this is a skin infection. Cellulitis or infection of the skin can cause warm, red and tender skin. A fungal infection, like jock itch is also common. Probably the most common condition is actually herpes. This often develops into vesicles that can be painful or itchy. Herpes is a sexually transmitted disease. Finally, this could be a sign of a full body skin condition like psoriasis.
The other condition to consider is vaginitis. While it most commonly has vaginal discharge--it is not unheard of to have the itching first. Vaginitis can be from many causes but the three most common include a yeast infection, bacterial vaginosis (a change in bacteria in the vagina) and trichomonas (a parasitic sexually transmitted disease). Chlamydia and gonorrhea can also do this.
There are many simple causes for what you note, but there are some serious conditions that should be easily ruled out. Talk to your doctor.