It's possible to have a functional (not absolute) B12 deficiency, where serum levels of B12 are normal, but the body isn't able to actually use the B12. Better indicators of this kind of deficiency are high levels of homocysteine and methylmalonic acid.
What kind of B12 are you taking? Is it methylcobalamin (the active form of B12)?
Also, as bucci mentioned, you should take a form of folic acid. Preferably the active form, L-methylfolate (aka Metafolin/Folapro/5-MTHF). Or folinic acid.
Post Edited (vitamink) : 5/17/2012 11:11:59 AM (GMT-6)