welcome to the forum
In Bipolar disorder
, there are alternating manic and depressive symptoms.....
In your case it might be the reason that you were diagnosed initially as having depression
and were prescribed antidepressants (when actually you were experiencing depressive part of bipolar disorder) ........ so you were not initially diagnosed as bipolar disorder.... and it sometimes happen in initial stages
Now when your diagnosis is changed.........your treatment has been changed....
Consult your psychiatrist
for all the doubts you have regarding treatment change