What Causes Flea Like Bites All Over The Body Leading To Pain?

My niece had what we thought was flea bites on her legs this summer. Since then the bites or irritation has spread all over her body. She has seen a dermatologist, had biopsys taken, and life threatening diseases have been ruled out. Scabies have also been ruled out. She has been placed in a light box several times, been on steroids, cortisone, and has been taken prescription allergy meds. Nothing is working and it keeps spreading and getting worse. She can't sleep, itches constantly and is in a lot of pain. Could something have been missed? There were no blood tests done. She is completely covered with these red insect bite like bumpers that start under the skin then blister and scar. Please help!!!!