I seem to be fatigued often?

Many, many things: You're talking about one of the most common complaints out there. Many things can cause fatigue, from as simple as poor sleep habits to more serious health conditions. Basically, you need a workup, including labs and maybe an ekg or chest xray or even a sleep study. There really is no other way to figure this out.

Many possibilities.: There are innumerable medical, nutritional and emotional conditions that include being tired as a symptom. These range from simple issues to those far more complex. A good checkup and blood testing would be a good starting point.