Volunteer, do an internship or dabble in courses. Finally, from your research and exploration, a viable career choice should emerge. Finding a career can be difficult, frustrating, even depressing. Each person has her own timeline and develops at different rates. People get locked in on what they think they should be doing and get some sort of paralysis because it isn't something that they want to do.
People also feel social or familial pressures.
The idea of staying with one career until retirement is highly unlikely. Don't think there is only one right career out there for you. All have some aspects that you love but others that you must grudgingly accept. Gar's final piece of advice is to surround yourself with supportive people, since you may need them to get you through the tough times.