B12 deficiency symptoms are very very similar to CFS/ME symptoms. I don't know enough about b12 anaemia but I know there are groups out there who say the injections given by the nhs aren't strong enough. Maybe someone on here will know more.
I'm too cotton wool headed (I have cfs/me) at the moment to reply properly so I hope others can reply to your post in the morning. Just couldn't not answer and wanted to let you know you are not alone and I completely understand how you feel. It's a cruel awful illness made worse by having to constantly explain and justify yourself because it's invisible and people can't seem to grasp illnesses and pain that they can't see. If they could feel how you feel for just 10 minutes they'd be shocked. I'm very sorry you're dealing with this. 
Just off the top of my head, and please research any advice as it depends on the individual, but things that have helped me are
Vitamin D supplements (high strength gel capsules)
Q10 (200mg)
Magnesium at night.
A teaspoon of D-Ribose powder in water each day. (Get it from body building/runners websites. I like My Protein)
Sour cherry juice (concentrated kind from Holland & Barrett. 30ml (ish) Must be the sour kind) in a large glass of water or whatever you need.
Weirdly it's the cherry juice that has helped the most although it sounds like complete nonsense. I was very surprised. It helps my brain fog and muscle/joint pain immensely. May not do anything for you but well worth a try. There's been proper studies that suggest it's good for inflammation (in arthritis type conditions). Do give that a go, there's no harm done if it doesn't doesn't help.
Sorry I can't give any advice on how to make it completely better. I wish I could. If I ever meet a genie I intend to use all three of my wishes on making this awful condition go away for all of us.