your question raised some awareness for me because before Ive never paid attention to "moons". However as far as Im concerned b12 malabsorption is quite common, primarly because the supplements are not being taken with something that make the body alkaline in order to absorb it. Next time you can try to take them with a glass of water with a squeeze of lemon aside (if you dont like lemon, orange is good too). have you ever consider shots? They are faster and effective.
Moreover to the emotional cause, could it be a that you need more time and not to push yourself so hard? Im guessing, but since a lack of energy would cause you to take it slow and more gentle it might be the case. I hope it was helpful!