Irritation in vagina???

So about a week ago I had a really bad itch that turned into painful stinging around the opening of my vagina. I went to the doctor and got my pee tested, and it wasn't a yeast infection or cystitis! Recently it has come and gone, and it's freaking me out because no one knows what it is. It hurts around the opening of my vagina as well as my urethral opening, but nothing in the tests show any signs of infection. Anyone know what this could be? It hurts really bad!