Hypochlorhydria (low stomach acid) results in any number of conditions including
nutritional deficiencies, insufficient pancreatic digestive enzymes, heartburn, acid reflux, gas, bloating, constipation, diarrhea....the list of possible symptoms is extensive.
Correcting a thyroid imbalance can take some time so in the meantime there you could try apple cider vinegar or betaine HCI with pepsin supplements to make up for stomach acid insufficiency.