A 20 year old man has presented with increased alcohol consumption and sexual indulgence, irritability, lack of sleep, and not feeling fatigued even on prolonged periods of activity. All these changes have been present for 3 weeks. The most likely diagnosis is -
Diagnostic criteria for mania
Three or more of the following for at least 1 week:-

Inflated self esteem or grandiosity     
Decreased need for sleep        
Overtalkativeness   
Flight of ideas 
Distractibility
Psychomotor agitation or Increased goal-directed activities
Excessive involvement in pleasurable activities

Coming to question
This patient has (for 3 weeks):-

Decreased need for sleep
Excessive involvement in pleasurable activities (sexual indulgence, increased alcohol consumption)
Increased activity (prolonged period of activity)

Diagnosis is mania.
Alcohol dependence
Schizophrenia
Mania
Impulsive control disorder