My 5 Yr Old Niece Has Strep Throat And Got

My 5 yr old niece has strep throat and got scarlet fever. The doctor gave her 2 small bottles of amoxicillin. She had a reaction to the medicine and broke out. Her lips are very chapped, she has a rash everywhere, it hurts her to go to the bathroom because she is so raw in that area. It's been almost a week, and she hasn't gotten any better. Her mother said the doctor said it was normal but I am unsure. She's been vomiting, and doesn't eat. She just wants to lay down all day. Today she was laying down and said she couldn't move her neck to look at me. I don't know if it's from just laying down in the same spot for a while, or something else. I'm scared that she isn't getting any nutrients and that's why she's so weak. I don't want her to keep going days without eating anything.