Suggest Treatment For Allergic Skin Reaction

My 16 year old daughter recently had an allergic reaction. She experienced excessive itching all over her body(her skin started to peel and a red rash appeared). Some of the areas that it he d the most included the back of her neck, the outside of her ears, inbetween her legs, and under her eyes. Also, she was vomiting constantly for about 12 hours. The next morning the vomiting had ceased and I took her to our primary, who suggested she had serum sickness from a prescription of amoxicillin she finished about three weeks prior for a sinus infection. Also, they took blood, gave her a shot to stop the itching, and suggested she take zertec. The next day the itching hadn t stopped so I called up the doctor again and they told me to take her to the ER. I took her there and they said that it was impossible to pinpoint what was causing the reaction but prescribed her with ranitidine, prednisone, and hydroxyzine. The itching ceased within in 12 hours. But now she had a fever of 100, feels lightheaded, is vomiting up everything she eats, sleeping almost all day, and looks very pale. I don t know where to go from here. Should I stop the antibiotics? Also, she s missed 4 days of school because of this and it doesn t look like she s heading back anytime soon.