/ADHD was thought for many years to just be a symptom of children, that tended to resolve as people matured. Continued close observation of affected children, however, has demonstrated that a significant percentage, possibly more than half of those children, will continue to have the disorder even after becoming adults. The difference appears to be that the symptoms are more subtle in adults, and are thus not as readily recognizable.
The fact that you have been so high functioning for so long (given your history of already completing some graduate education) indicates that your specific case might not be related to a disorder, but might be something more subtle that is occurring in your work or home life. To properly diagnose ADD as an adult, there must be inattention, distractibility, impulsivity, and increased motor activity that disrupts normal activities and is present in at least 2 different environments (such as work, home, social situations, etc). If your poor concentration occurs only at work, it would not be sufficient for a diagnosis.
The best option for you would be to discuss these questions in more detail with your primary care doctor
, who will be able to ask you the appropriate questions and then refer you, as needed, to the appropriate specialist for further discussion and treatment options.