Your thoughts on his recommendations? I am sorry I do not trust most doctors with my diet as they are not trained for that. They are only trained for medicating.
I'd question any injection unless your B12 deficiency was very low and/or you have a known medical condition which doesn't allow absorption of B12 unless by injection.
Once you have finished the initial trial of B12 injections, start taking pills. After a couple of weeks then have blood work to reassess your B12 levels. There have been a number of peer reviewed medical journal articles showing that oral vitamin B12 is just as effective an injections - your doctor may not be aware of this. Here is one http://summaries.cochrane.org/CD004655/oral-vitamin-b12-versus-intramuscular-vitamin-b12-for-vitamin-b12-deficiency
Of course this only works if you do indeed take your pills faithfully - if not, then an injection every three months may be the best solution for you.
If it's of no consequence to your health otherwise, and I'll ignore the blasting for this, eat a little meat/fish every once in awhile or do something else as opposed to getting a shot for the rest of your life.
News flash: Most of the population (which eats TONS of meat and fish) is B12 deficient. Please don't eat meat (and risk your health and that of the animals) for that reason. Just take the damn pill.
As I mentioned above, I'm one of those who ate tons of meat and fish and had a serious B12 deficiency
. Don't eat meat; the only safe way is to supplement.