Welcome to NeuroTalk.

You don't need shots to supplement B12. Here is a long thread with alot of medical links including to Dr. Snow, who is an expert on the subject:

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

Near the end of that thread is an article from Dr. Snow that states he found a small number of people who seemed normal with B12 levels from testing, who still benefited from supplementation.

Oral forms do work, if taken on an empty stomach. Use the methylB12 form which is active in the body, not like cyanocobalamin which is synthetic and requires methylation.
Some people lack the enzymes that methylate folate and B12 so using the active forms works better for them. (it is called the MTHFR mutation).

Since there is no upper limit dose placed on B12 you can take it yourself. There have been no studies ever showing toxicity to it.

Since you are fairly normal you can start at 1mg (1000mcg) oral daily, on an empty stomach. Only about 10% or less of this is absorbed in people with no active intrinsic factor.

There are other nutrients that help with PN symptoms. B12 is not the only player.

http://neurotalk.psychcentral.com/thread121683.html