Sheila,
Go to «good» natural product place near you and ask for a complete B complexe supplement with a little vitamin C in it for better absortion, Vitanime B12 is water solubre, it will store itself in your liver but for a very short period of time so you need to get it daily.
I suggest you take it very slowly like haft a dose per day (not much, maybe taper it even more 1/4 dose per day only...) first and see wait 36-48hours, if ok, increase it until you take the daily normal dosage..
dosage is about 2.4 mcg daily for adults, a hair more for older forks.
Normaly if someone eats well you Bs intake should be enough but a little extra should not hurt.
Let us know what you find.