Before going on WW were you drinking a lot of non-diet soda, and are you now drinking a lot of diet soda? It wasn't clear from your reply. Like MSG, a lot of artificial sweeteners may have neurological effects. Maybe you need to avoid them. Try to think of the actual changes in what you are eating, not what your weight is. You might find a clue there.

I agree that it is not fair that you seem to have a choice between weight loss and tremor. Maybe you can get your neurologist to refer you to a really good clinical nutritionist with experience in neurologic conditions. Are you sure you are getting enough B-vitamins? I really think you should consult with your neurologist again.