Vitamin B12 is important for cell reproduction, blood formation, brain development, and bone growth. Individuals suffering from the symptoms of low vitamin B12 (or pernicious anemia), such as depression, exhaustion, anemia, and poor memory, may ask their doctor about vitamin B12 injections.  The physician will draw blood to measure the total blood levels of vitamin B12 in your body, and if they are low then B12 injections may be an option. Vitamin B12 injections contain a man-made form of vitamin B12 called cyanocobalamin. You should also speak to your doctor about allergies or other conditions which may have an adverse reaction to vitamin B12.  Though you can self-administer vitamin B12 injections, the safest way is to have someone give you the injection after being trained by a healthcare professional. 
To more permanently block a nerve, you would need to inject the nerve with a "destructive" agent, rather than just a local anesthetic. The destructive agent could be phenol or absolute alcohol, or anything else that is outright toxic to the nerve. Essentially, injecting a destructive agent onto the nerve can intentionally "kill" or destroy that nerve, or at least a portion of the nerve. If that nerve was carrying painful signals to the brain, then theoretically the signals should be stopped. One of the problems with destructive agents is that often they are toxic/destructive not only to nerve tissue, but also can cause damage to adjacent soft tissue structures in the body. Thus, they should be used with caution. Another potential problem is that even if you destroy a nerve at one point along its pathways, the more central portions of the nerve are still going up to the brain, and some patients might develop the de-afferentation pain syndromes (similar to the way that someone with an amputated leg might still feel like they are having pain in the amputated foot, even though that foot no longer exists, but indeed the nerves which previously carried those signals from that foot certainly do still exist in the spinal cord and brain).