B12 may not be your problem. It could be lack of iron, lack of salt and potassium, lack of magnesium, lack of the right foods.
I suggest you see your GP and tell him about it.
I wonder if you could complete your profile settings that ask for details on type of diabetes, treatment, and medications.
It would help us all to reply properly to you. I can see from earlier threads that you are T2 and on Gliclazide and glucofage (Metformin) but if these details were in your profile it would help.