Welcome to ThisIsMS, Amy. We cannot dispense medical advice here, but we can offer suggestions from one friend to another. I am a firm believer in second opinions. Start with your GP or internist, someone you trust and who is willing to work with you as a "disease detective." If necessary, find a new one. I think it is more logical to use your GP as your case manager; he may be more appropriate for conducting a baseline thorough physical exam and blood tests. His appointments are less costly (and more easily scheduled in a timely manner) than the specialists (neurologists) and a GP may actually be better at recognizing or ruling out conditions with similar symptoms.
Discuss with your GP the possibility of insulin resistance (your leg muscle cells may be insulin resistant and not allow glucose, which is your energy source, to enter the cells; could this be the reason for your left leg weakness?). You mentioned leg weakness and hand tremors seem to come and go; have you noticed if this coincides with eating sugar?
You mentioned having an enlarged thyroid – most physicians do not test beyond the Free T4 hormone level, if it appears in the normal range; it is more thorough to test for Free T3, Total T3, Reverse T3, and antithyroid antibodies as well. With the enlarged thyroid, you may well have a problem there. In fact, some people think MS (though this is probably not your diagnosis) symptoms are caused by thyroid hormone imbalance (for example, The MS Solution by Kathryn R. Simpson).
All the best.