8 Year Old Female Sick With High Fever Last 4

8 year old female sick with high fever last 4 days, stomach pain, nausea, vomiting once (bright yellow) tenderness lymph nodes/glands, spotted tongue, and now breaking out in hives. What is wrong? Urgent care 2x and ER once for possible appendicitis, throat culture, ultrasound, bloodwork, all results came back clear. Claiming a virus... a virus of what?!?!? Shes now on day 2 of hives all over her body.