What is fatigue? and can anxiety cause it?

Being worn out: If fatigue is from hard work, it is simply like hunger after some hours of fasting. Then you rest/sleep or eat and balance is restored. If fatigue comes w/o labor (even mental), it can be anxiety which is a sort of mental task - even if fraudulent. So, try to find a CBT therapist. At your age it's a great idea to learn skills to avoid, reduce and manage anxiety. Try it before a pill.