The multiple symptoms that your are having strongly indicate that you are having a systemic
disorder. But as all the tests for autoimmune disease have came back as normal, you should also be checked for other systemic disorders like celiac disease or whipples. These can also present with intestinal / abdominal as well as muscle weakness, weight loss, anemia etc.
I guess you have been checked for Rh factor too. Sometimes, the Rh factor may not be positive and you would aonly get an elevated ESR and a CRP.
I think you should repeat some of the tests like CBC, ANA titer, CRP, RH factor, Anti ribosomal antibody
, anti centromere antibody.
Sometimes autoimmune thyroid
disorders like Graves disease or Hashimotos thyroiditis may present with abdominal symptoms due to high thyroid hormone levels. Please check your thyroid profile.
You should consult a team of doctors including an immunologist , rheumatologist and a hematologist. I think all your problems are related, its only that you are not getting the correct clue about the specific diagnosis.
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