Can you call your Gynecologist for an appointment? I am concerned about the rash and itchiness on the skin around your vagina and inner thighs, and this should be medically evaluated by a doctor.
Have you had any sexual contact prior to the itching? There are many sexually-transmitted infections (they clear up with proper medication---don't worry!) that cause itchiness around the genital area.
(It sounds like your dermatologist only looked at the area underneath your arm, correct?) Did your dermatologist tell you how long it will take to feel relief (it's "only" been two days on your medication), and if s/he said immediately or within a day, you should call your dermatologist Monday AM and update him/her on your (lack of) progress.