Sorry to say, that different drugs can affect people in different ways, so what happened to any of us may not be applicable to you. I've had a gain where others have had a loss, and a loss when others have gained.. go figure our crazy bodies.
Here are a few links for you to do some research about Zoloft:
http://www.zoloft.com/ - the drug's website. Probably the best place to start.
http://health.yahoo.com/health/pdr_drugs/0373/0.html
Another valuable resource is your pharmacist... call him or her up and ask.. they really know their stuff.
One thing I DO notice that drugs can do very easily is make you not pay as close attention to things as you might normally have. Ask yourself, am I journaling or keeping track of my points . calories.. or whatever fits for your food plan? Are you getting exercise? The new guidelines are recommending 1 hour a day 6 days a week for weight loss. .. are you in the ballpark of this amount? You may have to shake up your food plan/exercise routine to combat the drugs side effects.. or else ask your doctor about another drug.
Good Luck Maribeth