Thanks for contacting with your health concern
1. Without being able to examine you directly, I'm of the following opinion keeping in mind your age and drug history:
i. As you are diabetic and on metformin do remember that nausea, burping/ flatulence, indigestion [which you are experiencing] are documented side effects of the drug.
ii. vitamin B12 deficiency
[intrinsic factor] level also decrease as the age progress and Metformin also causes malabsorption
of Vitamin B12 thus they are more prone to atrophic gastritis
. [check with Vit. B12 level]
iii. One major effect of Metformin is 'lactic acidosis' [LA], which can occur in presence of renal failure
and alcoholism. [as you are in advance age which causes the renal function to decline thus check with kidney function test], since LA can cause nausea. [check with lactic acid test]
2. other factors which one has to keep in mind are:
i. As the age progresses people tend to produce less acid [HCl] called as hypochlorhydria
resulting in impaired/slower digestion. [and veggies are most affected since vegetarian diet are low in protein which can result in decreased production of HCl]
ii. Lactose intolerance
3. So it is best to put you on a dietary regime which is free from causing stomach upset/burping, like
- Lactose-free product like soy milk, lactose-free milk, potato, rice, barley, margarine without butter/milk, fruit and vegetable juice, plain herbs and spice, jellies, jams
- maintain a diet with low glycemic index/low fat.
- eat smaller meals regularly and chew food thoroughly.
- take a multivitamin
which includes B3 and B12.
. increase intake of fiber and omega 3 fatty acids
PS. It could be IBS [irritable bowel syndrome] so consult call your doctor or a Gastroenterologist for necessary examination and investigation, since it can be symptoms of underlying illness or infection which require medical intervention.