Vitamin B12 deficiency is usually not a lifelong problem. Usually it resolves within months to a year. Commonly gastritis (acidity/gas trouble) and dietary deficiencies cause vitamin B12 deficiency. So take diets which are rich in B12 such as eggs, milk, cheese, milk products, meat, fish, shellfish and poultry. Some soy and rice beverages also contain B12.
Next Steps
Try nutritional and dietary changes.
Consult a gastroenterologist also if symptoms do not resolve.