Depends on cause... There are lots of reasons for B12 deficiency, but can you offer more information about your medical history so we can help you learn why your B12 level is down? B12 can be supplemented orally, by nasal spray, by injection appropriate to the cause of the B12 deficiency. Talk with your doctor about which formulation is appropriate for you. Or do you have a parasite that needs treatment??
Absorbtion. A common reason for B12 deficiency is the inherited or acquired deficiency in the ability to absorb the vitamin. If you do not make enough of the intrinsic factor required for it to be absorbed, you can consume bucket loads and never overcome the defect.Please confirm the cause of your problem with your doc so you can understand his/her treatment approach.
Anemia. There are many reasons to be anemic (low blood count, specifically Hemoglobin and/or Hematocrit). Interestingly, you didn't mention that you're deficient in B12, just that you've been diagnosed w/B12 deficiency. But Folate (folic acid) could masquerade as another possible cause. And of course, energy drinks are not intended to serve a source of vitamins. That's just advertising jargon to convince you to drink.
B12 absorption. Vitamin B12 has many important functions; one of them being instrumental in red blood cell production. To absorb B12 your stomach makes a protein called intrinsic factor (IF). The B12 binds to If at the top of the intestine and then is absorbed at the end as a complex. Low B12 is usually from low IF. Low stomach acid, gastritis, bacterial infections, prior stomach surgery like gastric bypass. .