I get tired when THINKING about life? I have no REAL motivation? I don't know WHAT I want to do?

Wow. Motivation. If anyone can tell you how to get it they should bottle it up and sell it 'cause they would make a fortune. 17 is so full of promise. You are starting a life as an independent being. No wonder you are so confused. Did you know that most people change their jobs or careers 7 times in their lifetime? You sound like a very astute person. This is what I think you should do. Be a 17 year old. Enjoy life because it is the journey that is the most important. Observe people and nature and keep putting one foot in front of the other. Don't compare yourself, just be yourself. Live in the moment and feel it, the good times and the bad times. Don't stop yourself from doing things while you are trying to figure out what to do. See the movie, "The Yes Man" and read Stephen King's "The Stand". And believe in yourself 'cause I think you are gonna be more that just fine. Good luck!