Hi stayingafloat, The biggest thing that stood out in your post here is that you have only been taking Zoloft for a few months. So, I would question what dosage your on? The reason is that most times if people have their PCP prescribe their antidepressants they start off on a low dose and end up usually taking 150mg per day, which is fine for a lot of people but, for those of us who have Major Depression or go through a major stressor in life such as a health problem then the dosage certianly would need to be adjusted. To help get us over that hump.
Dont worry so much that it isnt working. I would just speak to your prescribing physician and let them know how your feeling and ask if a boost in dosage is availiable for you. The maximum dosage of Zoloft recomended by the FDA is 300 mg per day and of course your physician can prescribe above this if they feel it is medically necessary but very rarely will you see Zoloft prescribed in this high amount. So if the higher dosages arent working then usually the doc's will switch meds at that point.
But since you felt the Zoloft was helping until your surgery I would ask for a increase in dose and see if that helps first before you consider changing meds. I hope this helps and let us know how your doing dear... 