Well, I am sorry for your loss.
I worked on the defense side of these things, and it has been over 15 years now since I was in Atlanta. So, I don't know any Plaintiff's firms that specialize in Med Mal. (There is one guy I know who has his own shop, and he handles wrongful death claims i.e. he is pretty good - but I don't see any indication he specifically works Med mal claims.
Off the top of my head though - make sure you keep records (autopsy included), and document things/memories now - get the medical records from the doctor. It will be an uphill battle to show that drugs caused the death (without knowing the prescription - you might google to see if there are related deaths, and might find some firms with experience pursuing those claims). You'll have to show that not only was the death a result of the pills, but that standard care of a physician required certain tests, and that those test results would have contra-indicated the use of the weight-loss pills.
One of the first hurdles you face in Georgia is that any Med Mal suit must contain an affidavit of an "expert competent to testify" (which is just a fancy way of saying, the expert must be an expert in the same field as your claim). That is a tough hurdle to clear - though good plainitff's firms can generally get an affidavit from "somewhere" to support a claim (assuming the firm believes its a worthwhile case).