I have fibromyalgia, but no autoimmune diseases - though I do have a strong family hx. of them including PA, RA and graves.
My B12 level was checked a few months ago with a low normal result of 400. However, I had been megadosing B12 for 3 months before that level taken - using tablets as well as liquid held under the tongue.
You should get those tests done to see if you have it. If you do then monthly injections can help you. If you have PA then your body will not absorb the B12 from vitamins or tablets. A lot of people have graves and other autoimmune diseases along with PA . With a family history of graves you may want to keep an eye out for it.