Welcome to healthcare Magic!
Your vit.B12 levels are crucially low and you seem to be having the peripheral neuropathy
and spinal cord
dysfunction due to this.
your doctor has planned a good regimen of vitamin B12
replacement. You should get the injection regularly and oral treatment as per this schedule.
neuropathy is a difficult problem and is very slow to recover even with accurate and best treatment because apart from the replacement of the vitamin the nerves need to heal the damage that have accumulated probably over many months period and nerves are the slowest healer in the body needing months to show response.
Breathing problem is not a feature of vit.B12 deficiency and may be due to respiratory or cardiac compromise simultaneously.
You should get a physical examination, a chest xray and an ECHO for the diagnosis of the respiratory problem.
I hope the advise would be informative and useful for you.