My 13 Year Old Was Diagnosed WithEBV 2 Weeks Ago.

My 13 year old was diagnosed withEBV 2 weeks ago. See woke up last night with a pain level of 10. We took her to the ER. After 4hrs the doctor said that they could not find a cause of this pain.They said it was anxiety and it was all in her head.She was so upset because she feels like no one believes her that she is sick. I am at the end of my rope.Please give me some advice