You need to take B12 on an empty stomach. It won't be absorbed with or after food.

Without knowing WHY you are so low, one has to wonder if you have
1) inherited pernicious anemia or autoimmune damage to the parietal cells of the stomach?

2) or, taking acid blocking drugs every day, or metformin?

3) or having the MTHFR mutation which is becoming fairly common (up to 40% predicted to have this).

4) malabsorption due to inflamed intestines (Crohn's disease) or
gluten intolerance.

With #3, you would need activated B12, called methylcobalamin.
And activated folate, called methylfolin. (Metafolin)
People with the mutation cannot activate cyanocobalamin in the tissues, so it is useless.

So cut to the chase and use the inexpensive Methylcobalamin.
I'd do 5mg on an empty stomach 1 hr before breakfast daily.

This should raise you up within 3 months to about 1000pg/ml

500mcg a day is very low and one study that measured absorption found only about 9 mcg were absorbed.
This is the table published in the study:

http://www.ncbi.nlm.nih.gov/pmc/arti...able/T1/#TF1-4

Taking orally most approximates how B12 is absorbed and utilized from food.

You can do the injections if you choose, but they are invasive and expensive and use the old cyano form, mostly.

You can buy methylcobalamin now at Costco and Walgreen's.
And online at various places. iherb.com or Swanson's, etc.
iherb also has the MetaFolin. iherb is a discount high quality supplier that carries all sorts of brand name products at substantial discount. For many years it was one of the few online sources for methylcobalamin. Now the B12 topic is more disseminated and so other places now carry it too.