Have any of your products changed formulas - think "new and improved"?
What kind of products to you use? I'm assuming the basics - toilet paper, tampons/pads, etc? Maybe baby wipes or "feminine wipes"? Is everything scent free? Dye free? You can develop an allergy at any time, so maybe that's what is happening here.
If you are douching, stop doing that. That can easily disrupt the very delicate balance of the vagina.
If you use the same body wash that you use on your body to wash your vagina, stop doing that, too. The vagina is like a self-cleaning oven. The good and bad bacteria work together to keep it clean and healthy. All you really need to do is use a washcloth to wipe the exterior.
Make sure you are wearing cotton undies, or at least undies with a 100% cotton crotch.
If you get waxed, asked if they've changed products.
Try to think of everything. It may be something really simple.
It sounds like you have a yeast infection. If I am correct buy an anti fungal cream and that should help get rid of it soon