What is the best solution for vitamin b12 defeciency??

Depends: If you are B12 deficient due inadequate dietary intake, as may happen in a vegan, you may take B12 orally. However if the deficiency is due to poor absorption, you should take B12 injections of about 1000 micrograms every three months or so. Given that you are deficient in vitamin D also, I would recommend B12 by injection.

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??