What Causes Vaginal Burning Sensations With Pressure?

I have been having some burning down there for about a month now. I went to my Dr. because at first I thought it may be a UTI. The test came back I did have a UTI so she put me on an anti-biotic. Three antibiotics later, I didn t feel any better at all. She prescribed me another, and said to PUSH THE WATER intake. Which I ve done. There have been a few days where I ve had REALLY BAD lower back back so I though maybe I have a kidney stone as some of the symptoms are similar and I ve had one before. I feel much better than I did a month ago, but when I sit all day at work, it still burns...almost like a burning pressure. I don t what else it could be and I can t afford to be having a bunch of tests done. Any ideas or suggestions?