What are the benefits is any of a B-12 shot

My doctor gave me one the other day and I didn’t feel any different. He is going to give me one every week for a few weeks.
Do they have any benefits?

B-12 shots are lifesaving if you have pernicious anemia. If you don’t have that particular variety of anemia, there is little credible evidence that the injection does much of anything for the vast majority of individuals. It is often touted as being helpful in relieving fatigue, but there is no good evidence to back this claim up.