Suggest Treatment For Rashes Throughout Body, Vomiting, Fever, Headache And Diarrhea

Hi my daughter has skin rash on all her body from head to toe and low fever with vomit / diarrhea. She had vomit with fever and diarrhea about 6 days ago that resolved after48 hrs. 4 days later ( last night) she had fever,stomach ache, head ache , mild vomit and mild diarrhea In addition to the previous symptoms now she has the rash. This morning I saw her Dr who recommended Claritin and Probiotic. My daughter has been drinking a lot of clear liquids an saltines. She still has the rash , did not vomit but I m worried. Can a gastroenteritis cause also this itchy rash?