--there may be a number of things going on with you that are resulting in low B12; it seems unlikely that it wold be directly traceable to something like pernicious anemia (actually, not an anemia at all, but a lack of intrinsic factor in the stomach to break B12 out of food).

B12 is the only B-vitamin stored in appreciable amounts in the body--in the liver, actually. If you're getting B12 shots and feeling good for only a very short time, you must have no appreciable stores, and your B12 deficient body must be sucking up what's given to you in shorts very rapidly.

Of course, severe B12 deficiency is very serious--it can affect every cell in the body. You need to get B12 regularly. Current medical literature indicates oral supplementation in large doses--1000mcg to 5000mcg/day (I'd go for the higher end initially)--is just as effective as shots, if not more so, and supplies a much more regular dose. And it is relatively cheap; many of use on-line sites such as iherb or vitacost or swanson vitamins to have it (and many other supplements) delivered. Try to get the methylcobalamin form, rather than the more common cyanocobalamin form; it has fewer metabolic hoops to jmp through to be usable.

Meantime, we do have a lot of B12 experience around here--I want to give you some links, first to the B12 thread at the peripheral neuropathy board:

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

Also, our own jccgltenfrees Gluten File material on B12:

http://jccglutenfree.googlepages.com/b12deficiency

Rose (who used to post here more often) has set up her own website about her battle with B12 deficiency:

http://roseannster.googlepages.com/

And Paul Golding has excellent info as well:

http://www.paulgolding.id.au/THE_B12...rayalHome.html