Although I don't have answers for you, I can 100% identify with your problem!
I had severe memory loss, skin symptoms, depression, irratibility and low B12, I took 1000mg of B12 for 4 months, tested again and my tests said 147. Australia says that anything above 140 is okay so my doctor advised not to bother with B12 injections.
My mother is a nurse, she disagreed and has given me injections since then for 6-8 months (this is when my symptoms cleared).
I went back to the doctor to check my B12 levels at the end of the month and they were 245. My doctor told me I was not B12 defficient because I didn't have anemia and now I am fine and to stop with the injections, referred me to a psychiatrist and sent me on my way.
It would be great if someone who was actually knowledgable about B12 was available to lend some advice. What next!?