I have been extremely fatigued lately and cannot figure out why. After sleeping 14-15 hours last night, and only being awake for the past 6, I m ready to go to bed already, it is only 7:30pm, and I slept this morning until 1:30pm. I have been very busy lately, I am not anemic and my thyroid is normal. I am on depression medication sertraline and my white blood cell count is off- my doc says I could be still recovering from an illness such as mono, but I am unsure of what could be causing this extreme tiredness. It s preventing me from daily activities.