I've been doing some introspecting lately. I'm at that point in my life where I'm starting to wonder if I'm on the right track. I'm a creative writing major at the moment, but it's not something I want to make a living out of.
So what to do when you don't know where to take your life?
There are a couple of things I've found that can help you find some direction.
The first thing I did was make an appointment with my university's Career Services office. Career Services departments usually have counselors on hand for just such an occupational identity crisis, and having someone to discuss things with can really help clarify the situation as well.
Another thing Career Services is good for is the Strong Interest Inventory, which measures not only your interests, but your personality and learning styles as well. It's helpful to go over the results with a counselor because A) they know what resources are available; and B) they can advise you on how to best utilize them according to your results.
If you're not enrolled in a university, most state Department of Labor offices will offer similar services.
Steve Pavlina has a pretty good article about finding your purpose on his blog. In my experience, his method works very well. Just expect to be surprised at what you find out about yourself.
Once armed with this knowledge, you'll be better prepared when meeting with that Career Services counselor, and you'll likely find that you have more energy when you're working towards your purpose.