And, I'm with you--I think that B12 level is rather low, and could be behind some of the symptoms you describe. That old reference range is rather outdated; most new labs begin the low end of the range at least around 400 and many in Europe and Japan at 500-550. The best labs have no upper end to the range--as you noted, B12 has no known toxicity level.

This looks like it might take further investigation at a teaching hospital or tertiary facility (if it is possible for you to get to one). In the meantime, I think it is good that you are supplementing; many of us here recommend constant oral methylcobalamin dosing in the range of 1000-5000mcg/day, rather than injections, as that way your body is regularly flushed with B12.

If you haven't already, you should come take a look as some of the following forums/threads here--a lot of literature, expertise, and commentary:

http://neurotalk.psychcentral.com/thread85103.html

http://neurotalk.psychcentral.com/forum119.html