@CrumblingCookie said:
Maybe it's time to up your scope before any more dabbling and to get an abdominal MRI to look for structural constrictions or masses and also your plasma levels of Ca, PTH, CT and a GI hormones panel at a specialized clinic.
As for GI hormones my initial thought would be to check for elevated somatostatin (constipation, lack of motility, steatorrhea; pancreatic and reciprocal gastric dysfunction). In the US they typically run a complete GI hormones panel which includes SST but it's more selective and specialized in other places. Weirdly, the symptomatic treatment for SSTomas is the SST-analogon octreotide, due to a high affinity to SST autoreceptors. You'd be a 1 in 40 millions /year case with that. Anatomically, surgical removal of such neuroendocrine tumors are far from elegant. Clearly it's better to not have one. I'd work my way forward by exluding possible causes step by step. Not sure what your state of insurance and medical services provision is like where you are (Eastern Europe). At this point I would try to (also) get a contrast-enhanced full abdominal MRI without further deferral.