It took me nearly two decades of problems before I got a SIBO diagnosis, via breath testing. But now I'm not sure how much stock to put in such tests, given the very recent paper https://onlinelibrary.wiley.com/doi/10.1111/nmo.14817 which suggests positive breath test results may usually be an artifact of decreased transit time more than any small bowel overgrowth.

I definitely sympathize with you on doctors generally being unhelpful and uncurious.