How do I prevent hives? Please answer!?

I've had hives for a little over a week. I'm still not sure of the cause and I don't think I will be able to find the cause. I went to the doctor's office and saw a nurse practitioner and she said that they won't go away. That kind of irritated me since I break out in hives every single time I take a shower. How do I get rid of/prevent hives? Please give detailed answers with as much information as you can provide. Thank you so much.