Lara
Just started today trying to do the same testing process for the much the same symptoms you listed. (details in my post: http://neurotalk.psychcentral.com/thread218283.html)
One article on diagnosing B12 deficiency that I found useful is at: http://www.aafp.org/afp/2003/0301/p979.html
It has a diagram illustrating the diagnostic path and test ranges are in both US and International measures.
All the best.