I highly suggest that you start by going to see your primary care doctor
or a psychiatrist
. Your primary care doctor could be a good first start, as they will be able to make a preliminary assessment. However, if they suspect attention deficit disorder they will probably refer you to see a psychiatrist, as most primary care doctor do not treat attention deficit disorder in adults (this is different for children, obviously).
Research on attention deficit disorder in adults is still emerging. What is clear is that most often the symptoms do not begin out of the blue in adulthood. Most adults with the disorder had symptoms that were present as children or teenagers, although these symptoms may not have been formally diagnosed. If you had no symptoms earlier in life, this lowers the probability that this is attention deficit disorder, and makes things like fatigue and stress more likely to be the underlying problem.
Symptoms of attention deficit disorder include distractibility, trouble staying on task, and problems with impulse control. In order to be diagnosed, usually these symptoms have to be causing significant social impairment, such as affecting your performance in college or your ability to perform well at work.