What Causes Itchy Red Rash On The Genitals?

Hello, I'm 29, 135 lbs. I recently started jogging outside. I have developed an itchy red rash on my genitals. I goes from my vagina to my anus. I went to the doctor a few days ago and she perscribed a cream for me to use (Nystatin and Triamcinolone Acetonide cream). the redness seems to have gone away some but it is still very itchy. I'm about to start my period and go on vacation where i will be caming for 4 days. I'm not sure what to do. Should i make another appointment with my doctor? Will i be able to use tampons when my period starts?