Having (myself & other family members) experienced incorrect diagnosis by drs & specialists in several areas of medicine inc mental, I am firmly of the opinion that getting a 2nd opinion is always wise especially when dealing with either a serious or lifelong illness/condition!!
But, that is sometimes hard to do - so first do not tell the 2nd dr that you are seeking a 2nd opinion as many tend to "agree" with their peers. Try to find a dr who is referred by a patient who says that the dr listens, thinks outside the square & is prepared to consider boith alternative treatments & alternative diagnoses.
Keep researching yourself (symptoms, family histories, treatment alternatives, alternative medicines etc etc) on the net via sites like google & yahoo. You might also look into auto immune disorders, & oddly enough "causes for weight change" can take you to some interesting sites & strange often unheard of conditions which can cause soooooooooooo many different things - again perhaps just worth a look see.
But please try to limit your questions to one on-going post as with just one question per site it is hard for the reader to get an overall understanding of what you are ssaying/asking/experiencing & so very hard for us to offer real help/advice. Whereas if you post your next question after this one or along with it then readers can get a more complete idea of what you are asking etc.