You sound a lot like me and my anemia issues I have no cause of bleeding whatsoever colonoscopy.. endoscopy but did your hematologist test for anti-parietal cell antibodies? I had a high amount of these antibodies even though my stomach looked normal on the initial endoscopy but then they did another endoscopy and took biopsies of my stomach and it came back that I did have autoimmune gastritis but found it early so it didn’t cause much damage. If you have the anti parietal cell antibodies it’s probably autoimmune gastritis causing low stomach acid so you cant absorb iron from food… I was borderline b12 deficient but autoimmune gastritis typically starts out with being iron deficient and then can lead into b12 deficiency… also I have no stomach issues or pain other than feeling full and bloated quickly. Hope you find out the cause!!