Talk to Neuro Physician on Pain After B12 Injections

My mother having headaches while sleeping at night, so Neurologist have done reports and found B12 as very low so he gave B12 injection 1000cu for 7 days then weekly for 4 weeks then monthly, Now the problem is its the fourth week and she is having soo much pain uthne bethne me, please suggest what to do for permanent relief, as pain killer only works for few hours only. She also have Cholesterol and also take Vitamin D3 and Calcium tablets