Medication effects are different for everyone. I can tell you that my experience with Zoloft was this: I started at 200mg. I was a MESS of agitation, anxiety, horrible fear/dread...a very, very negative and severe mania. Worse than I was when I started taking the stuff. Somehow I made it through a month in that awful state of being. Finally communicated with my p-doc. Dropped dose to 150mg. Still in a very bad state. Hung on with that for another month (it was sheer hell). Went down to 125mg...still in a very mixed-state horrible place. Changed p-docs. New p-doc told me that ssri's can set off mania (either positive or negative) for bipolar people, of which I am one. Dropped the Zoloft down to 100mg. I've been at 100mg for about a month and it seems to be more or less okay. Definitely much, much better than the higher doses.

You might be very sensitive to the Zoloft. Since you feel worse I think you have two options. Either you can stay with your current dose and see how you feel in, say, 3 more days OR you can contact your p-doc and see what s/he has to tell you.