I have been diagnosed with the autoimmune pernicious anemia, which is low B-12. I was accidentally diagnosed- I had been going to my doctor and telling him how physically tired I was- I literally could just about barely move. Luckily, I have a sit down office job, and often I was so tired, I couldn't bear to think of getting up to go to the restroom. Now that's tired. So, my doctor decided last minute to check my B-12, and found out that it was low. I also have a lot of autoimmune antibodies for this, which is what made the definitive diagnosis.
Something else I have found is that metformin depletes your B-12.
All of this to say is that B-12 will affect your energy level. When I get my shots (usually every 2-3 weeks), I feel a difference in my energy. It's odd, in my case, it's not like I go from way low to way high when I get my shot, but once I have my shot, usually the next day, I think, oh, this is how I "should" feel.
I don't think it would hurt to take B-12. I know typically you get your B-12 from red meat and dairy. In my case, I cannot absorb it fromfood, so I have to have the shot. | 
It is not as common as it used to be here in Mexico. There is a GNC in the mall here so I think I will pay them a visit tomorrow.
