Welcome to the board.
I would contact your doctor right away. Alot of antidepressants cause weight gain,but it is something that you need to talk to your Dr about
. He or she should be monitoring your weight,and if it gets worse then they will probably change your meds.
Here is some good info I found.depression.about.com/cs/weight/a/weightgain.htm
Good Luck and please keep us posted on how you are.
Chronic Depression, Panic Attacks,Anxiety Attacks,Anorexia