Yes you can still take them, and if you're energy is still low, i recommend you eat 7 dates everyday. Whenever you want, but preferably at breakfast. I hope it will help you! P.s: you can always do a little research on dates to see their nutritional value and if it matches with your condition.
Absolutely. There's no harm in taking vitamins. If your body doesn't need it, it'll just expel it. B-12 can definitely give you a boost. Talk to your doctor about your iron levels too. When I had low energy I found out I had an iron deficiency and taking iron tablets boosted my energy level.