I take a b12 shot every 2 wks, sometimes every week.
Sometimes I can feel the difference within that day and sometimes I can't feel the difference period. It just depends on how bad I feel or am flaring.
fff - I am NOT trying to practic medicine - but just as a general statement...
If a person has chronic fatigue, fibro, chronic pain - that person could certainly think about being tested for B-12 deficiency. I go to a neurologist who is a DO: so she is open to more natural therapy. I would think that if you are having problems your doctor would want to do some testing for things like that or Vitamin D deficiency. Wit D problems can cause terrible fatique - depression -and very bad muscle pain. I inject myself, in the thigh - it does not hurt ( as long as you let the medication warm up to room temp).
Sometimes a referral from your regular Doc to a neuro, endo, or rheumy could be in order (depending on your symptoms.
We all wish you well...