Vitamin D & vitamin B12 deficiency.

From d last few days I was having pain on my fingertips n fingers n went to a doctor who advised me to go fr a vitamin d ,vitamin b 12 n calcium test. And once reports came I saw that my vitamin d is 5.5 ( it has to be over 30 ) n vitamin b 12 is 166 ( it has to be above 186), however calcium levels were fine. Now the doctor has suggested me some injections for Vitamin d n b 12, in total 8 injections in d span of 10 days n after that some supplements which should go on for some months to curb this deficiency. My question is is it fine to go for thesw injections ? Or I can also fix this deficiency by only having supplements? N how can we fix this deficiency going forward so that this should not happen again. Please advice