VPL:
I personally would go to my PCP, and let him do a blood test. then go back to get the B12 shot.
The you can always take B12 tablets, upon PCP recommendation, of the proper dosage. My brother was B12 deficient and he got a shot. He felt tremendously better. Some things need to be administered thru a doctor, rather than self medicate.
Most of us have medical plans where we pay next to almost nothing, for doctor visits.
Just sayin.........because I know you love doctors, colonoscopies etc.
__________________
"It doesn't cost "nuttin", to be nice". 
MOM
I just want to do the right thing! Uncle Joe, (my hero).