jack russell licking her hair off

Hi i have a 5 yr old female jack russell. She is not fixed. She has bitten and licked off all of her fur on both sides of her hips to her butt. I have taken her to several vets and they do not know what to do to help her from doing this. Any help would be greatly appreciated. One told me to give her liquid benadryl. I have but it no longer works and i only give it to her when she is licking so bad that she cant stand herself. Please help.