Sadie,
I understand how you're feeling. Yes, do get a 2nd opinion, and a 3rd, 4th and 5th.....if needed. It took me seven years to get a diagnosis (and treatment). My SFEMG and antibody tests were negative. I was finally referred to Mayo Clinic and received a diagnosis after testing positive on the Tensilon test. They did not recheck my antibody test but did do another SFEMG (which was negative). In spite of the negative EMG, they opted to offer me treatment, including IVIG, b/c my Tensilon test was positive and all my symptoms pointed clearly to MG. And I responded to Mestinon.
So...don't give up. Do what you need to do to get the support at home that you need. Family, friends, etc. As you go to other appointments, it's helpful to take a support person with you--ideally your husband if possible. Always good to have a extra set of ears and he may recall symptoms and important clinical history that you may forget to mention.
Cate