15 YR OLD FEMALE.  NAUSEA, FATIGUE, LOSS OF APPETITE, WEIGHT LOSS OF 12 LBS OVER LAST 2 WEEKS (WEIGHED 120 TO START), BACK PAIN, LOW GRADE FEVER X 9 DAYS (99-100.8 ORAL). NOTHING SPECIFIC I CAN PUT MY FINGER ON BUT TODAY HAS SEVERE BACK PAIN.   RENAL INFECTION? MONO?  NO SORE THROAT.
As per you history, you may be suffering from PID (pelvic inflammatory disease), check for any foul smelling vaginal discharge. Consult a gynecologist