In a woman (or man) your age, a rash in that area is far more likely to be eczema than tinea versicolor, the fugus your doctor diagnosed and treated. Also, fungus doesn't itch andeczema does.
You should get re-evaluated and treated, most likely with a prescription-strength cortisone cream. Meantime, pick up some Sarna lotion (OTC)--excellent for suppressing itch.
Eczema is hereditary. Perhaps you had it as a child. It's unlikely to be allergi in nature. I would treat it first and see if further evaluation is worthwhile.
Best.
Dr. Rockoff