The reason why SSRIs gain cause weight gain is because SSRIs increase or interferes with the natural production of serotonin, which is not only related to moods but also to appetite. Serotonin is a hormone that gives you the feeling of satiety.
Depression is related to an imbalance in sugar metabolism, thus it is not surprising that one of the side effects of AD medication would be weight gain.
There are no easy solutions to depression but it needs to be treated at its core. Drugs and talk therapy cannot do so. You need to treat the REAL causes of depression!
Depression is a Nutritional Disorder" --->here
and discuss with a Nutritional Doctor or a Clinical Nutritionist.