What Causes Recurring Nausea, Sweating And Fatigue?

My 18 year old (high school senior) daughter keeps having nausea, sweating, low grade fever and lots of fatigue. She has had this several times and it has seemed to go away, but comes back.She had it on 1/12, but it was gone the next day. Now she has it again and it is worse. I have no idea what is going on..These are not the only 2 times she has had this. Do you have any idea of what is going on?
Thanks for your thoughts.
Marie E