I have a wonderful doctor. Even though blood test levels were high due to my taking b12 sublingual (over the counter), I was extremely tired and weak. She started my on b12 shots, starting to feel better but still not quite myself. First 2 injections are 2 weeks apart and than monthly along with my sublingual b12 . She told me that she will not be testing my b12 levels instead she will judge by how I feel for the frequency of shots.