What Is The Treatment For Itchy Hives All Over The Body?

My 3 year old has welts all over her face, back, neck, torso, hips and thighs. They have gotten progressively worse over the past 4 days. I've given her benadryl and put hydrocortisone on them but there are more now and spreading in larger areas. She does not have a fever and they itch. I'm unsure what to do now.