J.H.
I just read a great book on B12 deficiency - Could It Be B12?: An Epidemic of Misdiagnoses Sally M. Pacholok RN. You and your doctor might find this an interesting read. I got it through interlibrary loan but it is also on Amazon. That author suggests that despite the fact that science states that the sublingual is just as effective in some cases shots are more effective. According to her description it is a small needle and you can learn to do this at home. Also, if your body can not absorb B12 anything less than the megadoses of the sublingual will be ineffective.
Good luck