I was in a very similar situation. I was 21, studying mechanical engineering, not sure what to do with my life, but had high expectations. One book that helped me a lot was "I Could Do Anything If I Only Knew What It Was": http://www.amazon.com/Could-Anything-Only-Knew-What/dp/04405...

The book sounds corny, but it can help you get a better perspective on your life. Make sure to actually do the exercises.