Sadly there is a lack of knowledge among many in the medical profession about B12 deficiency and P.A. "It's a vitamin for goodness sake, you get it by eating animal products such as meat, fish seafood, eggs and dairy produce etc!"
You need to find out the cause of your deficiency.
Anyone at any age, can become B12 deficient. However, certain people are at an elevated risk. They include the following:
Vegetarians, vegans and people eating macrobiotic diets.
People aged sixty and over
People who’ve undergone any gastric and/or intestinal surgery, including bariatric surgery for weight loss purposes (Gastric bypass).
People who regularly use proton-pump- inhibitors. H2 blockers, antacids, Metformin, and related diabetes drugs, or other medications, or infections such as h-pylori that can interfere with B12 absorption.
People who undergo surgeries or dental procedures involving nitrous oxide, or who use the drug recreationally.
People with a history of eating disorders (anorexia or bulimia).
People with a history of alcoholism.
People with a family history of pernicious anaemia.
People diagnosed with anaemia (including iron deficiency anaemia, sickle cell anaemia and thalassaemia).
People with Crohn’s disease, irritable bowel syndrome, gluten enteropathy (celiac disease), or any other disease that cause malabsorption of nutrients.
People with autoimmune disorders (especially thyroid disorders such as Hashimoto’s thyroiditis and Grave’s disease) Type 1 diabetes, vitiligo, lupus, Addison’s disease, ulcerative colitis, infertility, acquired agammaglobulinemia, or a family history of these disorders.
Women with a history of infertility or multiple miscarriages.
Can you "see yourself" among any of the above people?
Treatment for PA and non-dietary vitamin B12 deficiency is virtually the same.
The symptoms of PA are the symptoms of the B12 deficiency that it causes. If the cause isn't dietary then it is an absorption problem so you need to find another way of replenishing B12 initially. Most absorption problems aren't treatable but a few are - notably h pylori infection - which would mean that once that has been dealt with you would be able to absorb B12 from your diet so wouldn't need maintenance shots for life.
I am not a medically trained person but I've had Pernicious Anaemia (a form of B12 deficiency) for more than 46 years.
I wish you well.