Update: Didn't read the latest letter (December 2021) from my gastroenterologist thoroughly. She wrote to my GP that it is most probable IBS I suffer from.
Hi, still struggling to get a diagnosis for my functional bowel problems in combination with all the other chronic all over the body symptoms. Did speak with the rheumatologist lately about Whipple’s disease (systemic bacterial infection) as a possible root cause of my chronic health issues (since my early childhood, I'm 53 now). Based on his current knowledge he doesn't think it's Whipple’s disease. However he's willing to do some additional examinations/test but no upper endoscopy of my small bowel or pcr test. That's why I ordered a PCR test for Whipple’s disease myself. Just trying to exclude possibilities (isn't that what the physicians should do?). Also because I felt well while taking systemic antibiotics (penicilline or tetracycline) and became sick again after the courses of antibiotics stopped. For me this is an indication that it is microbiome/bacteria related.
Addendum: The gastroenterologist, neurologist, psychiatrist and all the other consultants I did see throughout my life don't know what's causing all my symptoms. So got diagnosed with different disorders and syndromes without finding a root cause till now.