Your doctor means that you suffer from neurasthenia. Neurasthenia is a frequently misused term, the precise meaning of which is nervous condition consisting of lassitude, inertia, fatigue and loss of initiative. Other common symptoms that have been associated with a diagnosis of neurasthenia are restless fidgeting, over-sensitivity, and often an asthenic (i.e. very slim) physique.
Neurasthenia is an old diagnosis that today is very rarely used since other diagnoses have replaced it. Many patients that were formerly diagnosed as neurasthenics are believed today to suffer from neuroses, affective disorders, or other psychosomatic conditions. For these reasons, and to have your diagnosis and therapy checked by a psychiatric consultant, you should ask for a second medical opinion.