My 10 Year Old Son Has Been Sick For 10

My 10 year old son has been sick for 10 days now. It started with ear ache and sore throat with some vomiting. Then over the weekend more vomiting and now abdominal pain and diarrhea. Ears and throat are no longer an issue. He was put on an antibiotic last Monday but Dr now says to stop so this morning was last dose. He is looking pale and very weak. Tonight he says he's feeling worse. I noticed a small red circle on his upper back maybe an inch wide and I noticed another larger red mark on his neck tonight, not sure if that could mean anything. Any ideas what might be happening with him?