Get these, don't get shots or the synthetic b12. Dad's been taking these for over 35 years. Take them every 3 days or more if you want, you just urinate the excess b12 out. 1000mg's a chewable is more than enough.

http://www.amazon.com/Jarrow-Formulas-Methylcobalamin-5000mcg-Lozenges/dp/B0013OQGO6

Vitamin B-12 warning: Avoid cyanocobalamin, take only methylcobalamin

http://www.naturalnews.com/032766_cyanocobalamin_vitamin_B-12.html