I had a long talk one day with my son's gifted program teacher. She and her husband had been teaching gifted students for over 25 years when we had the conversation. Your son's behavior -- like my son's -- was not unlike many highly intelligent students she taught over the years. Not all are like that, but she is never surprised when highly intelligent boys, particularly, are high energy and only want to do what they want to do. She did not see that behavior as pathological but, intead, normal and to be expected.
The deteriorating behavior noticable starting at three months after beginning an antidepressant is a common timetable for the switch from wonderful hypomania to what can eventually be psychotic behavior. Appropriate treatment is discontinuation of the antidepressant, not the addition of any other medication.