Before and during your period, it's not uncommon for some women to get yeast infections which is what it sounds like is most likely what's going on, but since you are sexually active and have had unprotected sex, getting tested for STDs would be a wise idea. Also, since I'm gathering you're unfamiliar with what a yeast infection is like, you should have your doctor test to see if it's bacterial vaginosis (BV) and not a yeast infection, which is easy to treat and treated similar to a yeast infection, but the medication is prescription only.
Planned Parenthood has a really good info page on yeast infections/vaginitis, symptoms, things you can do to try to prevent them, all of that. http://www.plannedparenthood.org/health-topics/womens-health/yeast-infection-19854.htm — make sure you read the section on the symptoms of vaginitis.
One last thing — if you use scented pads or tampons or scented washes in the shower to clean down there, stop. Same with douching, if you douche, stop, it's more problematic than anything and your vagina is self-cleaning, it doesn't need douching. All of those things can throw things out of balance, cause irritation and create a great setup for a yeast infection or BV. Switch to unscented pads and tampons or if you aren't squeamish, a menstrual cup, use an unscented feminine wash for washing down there (though I have been told by 2 different OB/Gyns that a good rinsing in the shower, as in like a couple minutes spent rinsing with just water, is all that's needed and I do that a few days in a row but then I use a feminine wash after that because I just feel ick going any longer), change your pads frequently and use ones that trap moisture. When I was getting recurring yeast infections a few years ago, my gynecologist suggested going commando when possible and if I was wearing a skirt or something and couldn't really, wear cotton panties. Going sans undies helped a ton, the YI prob ended and that was that.
While you're waiting for your doctor appointment, you can go to the store and in the aisle with all the other feminine hygiene stuff, Vagisil makes anti-itch cream and also anti-itch cooling and soothing wipes. That might give you some relief until the doctor tells you what's up and how to treat it.