Hi I have Pernicious Anemia too.
I need my B12 shots I give to myself every other day or I get symptoms.
I live in Florida but get mine from Germany where you can buy them over the counter. The package slip says you cannot overdose b12 and there are no known side effects except maybe acne.
My acne is gone now after 2 years. I learned a lot at the first international b12 conference in Rotterdam last year. All the patients I met there were taking B12 shots every other day too.
There is some known testing issues with b12 tests for PA patients, I am not quite sure exactly how it works but what I understand is that some b12 binds to something that shows up in blood tests as high b12 (over 2000) for weeks after a shot but this bound b12 cannot be used well by the body. So even if the blood test shows high b12 after an injection most people still need their shots every other day. I found an article explaining this in medical terms: "False elevations of vitamin B12 levels due to assay errors in a patient with pernicious anemia" but would love to learn more about why b12 testing is not useful for PA.