I gather you haven't actually been tested for, and have elevated levels of D-lactate in the blood?
You could similarly just be describing symptoms that can occur with having dysbiosis, GI dysmotility, malnutrition, malabsorption, or any or all of these, and where you can have tolerance issue towards a few or many things.
If you can tolerate sweet corn or beets, you can use these as a simple test of your approximate GI transit times.
http://www.bigpicturehealth.com/a-corny-way-to-check-bowel-transit-time/
Your combination of conditions and symptoms paints a clear picture of it being more an autonomic dysfunction problem and a common occurence in those who have a POTS, EDS, MCAS combination is gastroparesis, delayed gastric emptying.
As well as gastroparesis, there is a growing body of evidence that NAFLD (Non alcoholic fatty liver disease) is strongly associated with autonomic dysfunction too and has a high incidence of having sudomotor dysfunction in one study, which is another indicator of autonomic dysfunction.
https://www.gastroendonews.com/Article/PrintArticle?articleID=44902
https://www.ncbi.nlm.nih.gov/pubmed/25614616
A QSART test is the usual means to test for sudomotor dysfunction. Did you happen to have this test done as part of an autonomic function test panel in diagnosing POTS or did they just do a Tilt Table Test? It might not add much to the overall diagnosis but QSART and Heart Rate Variability to Deep Breathing (HRVDB) can be abnormal with NAFLD. Abnormal HRVDB can be an indicator of vagus nerve dysfunction too, and often involves having low bp as well.
https://www.ncbi.nlm.nih.gov/pubmed/23626730
https://www.ncbi.nlm.nih.gov/pubmed/19768633
I see there's some other simple skin conduction tests offered for sudomotor dysfunction that might not require the involvement of being referred to a Neurologist, one from EZSCAN (Sudoscan) and the other is VITALSCAN (QBioscan), not sure how widely available they are though.
https://www.frontiersin.org/articles/10.3389/fendo.2016.00018/full
http://www.vitalscan.com/dtr_bioscan_sudomotor.htm
Colitis may be the key to your gut problems though and a possible explanation for this in your case is that a lot of people with EDS have visceroptosis (sinking of the abdominal viscera (internal organs) below their natural position) where lax ligaments allow the compression of vessels supplying blood to the bowel so colitis can be due to bowel blood flow being insufficient to meet metabolic demand during the digestion process so causing Chronic Intestinal Ischemia. (The three main conditions here are SMA Syndrome, Median Arcuate Ligament Syndrome (MALS) and renal Nutcracker Syndrome).
Get any doctor to listen to sounds in your epigastrium for any indication of a bruit (not everyone has this but can indicate a blocked bowel artery) but at least a Doppler ultrasound test to check the mesentery artery flow velocities is needed as a good screening measure but a CT Angiogram (prefereably with 3D reconstruction ability) is a more definitive test.
If it involves celiac artery compression by the diaphragm (MALS), the occlusion might only be seen on the exhalation phase of doing deep inhalation and exhalation.
https://gastroenterologen.no/2013/11/the-celiac-ganglion-artery-compression-syndrome-cgcs/
I have a lot of GI issues and don't tolerate either sodium bicarbonate (baking soda) or vinegar by themselves but when mixed together and diluted further with water, it's no problem.
(I also don't tolerate most real food but have gastroparesis, autonomic neuropathy, colitis, chronic intestinal ischemia and Nutcracker Syndrome. That's how come I know these vascular compression things affects those with EDS a lot (but which I don't have)).