I had a B12 deficiency before going primal and needed injections. I was surprised to find my levels were only marginally higher eating a primal diet. Just FYI - With your levels the injections are probably not necessary. I use an oral/sublingual methyl-B12 that seems to be working well (made by Jarrow).
Do you eat any organ meats or clams/mussles/oysters? These really are the most abundance sources of B12 and I don't think it is that difficult to become deficient if you are not eating those foods.
Awesome that you have a doc that considers 224 to be low. By CW standards in the US that is a normal B12 level. Hopefully injections or supplements will perk you up!