Hello and Welcome to ‘Ask A Doctor’ service. I have reviewed your query and here is my advice. Fatigue can be caused of different conditions. I assume your daughter has already had blood tests to rule out anemia (CBC and ERS), thyroid problems (TSH), and basic metabolic profile (ALT, AST, creatinine and electrolytes, lipids fasting blood sugar, etc). If all these tests have been normal than chronic fatigue syndrome can be considered as the cause of the fatigue she is having. Mononucleosis is accused as a possible cause of chronic fatigue syndrome. It is not very clear why it does so but studies have shown that patients with chronic fatigue syndrome test positive for mononucleosis showing that they have had it in the past. Depression can also cause extreme fatigue so an optimal treatment of depression with tablets and phsychotherapy might be needed. Trying to have a sleep hygiene with regular times of going to bed and getting out of bed is advisable. Exposure to daylight is important to help be awake during the day and regulate the sleeping pattern. Being active as much as she can, regular exercise, at least 30 minutes brisk wall three times a day might be helpful. Eating well and regularly is important. Getting involved in activities she enjoys as well. Hope I have answered your query. Let me know if I can assist you further. Kind regards, Antoneta Zotaj, MD