Welcome to NeuroTalk:

We have a B12 thread here:

http://neurotalk.psychcentral.com/thread85103.html

On it are discussions about every aspect of B12 supplementation.
I'd suggest you arrange to use Methylcobalmin for your oral or injection. Typically the injections are compounded by a compounding pharmacy.

Many people are turning up with the MTHFR mutation, and cannot methylate (activate) the cyano synthetic form. This would include folic acid too. There is a DNA test for this that you can request from your doctor.

Diabetics also get low in magnesium, as a factor of diabetes itself. Why they lose magnesium thru the urine is not understood at this time, but has been measured in various studies. So a good oral form, like SlowMag, one tablet twice a day will help that problem.
Here is their website with dietary suggestions also to increase foods that provide this mineral.
http://www.slowmag.com/
This product has a generic called Mag64, which you can have ordered for you at your pharmacy or buy online.

Taking acid blocking drugs for long periods of time, reduces acid in the stomach and that leads to poor absorption of magnesium, along with B12, folic acid, iron, calcium, zinc and some trace minerals too.

This is our PN forum with lots to read
http://neurotalk.psychcentral.com/forum20.html
We have been here since 2006 and before that since the late 1990's on another board location which crashed in 2006.
Over the years I have found quite a bit of useful information for nutrient replacement and also for peripheral neuropathy.