There was an interesting post from Dr John Briffa this week about the difficulty helping some people get rid of a persistent dry cough and the possibility that low B12 levels may be a factor.
I can echo what he says about this being an awkward one to treat. Often you can do it, but in some it improves but just won’t go. Like him, I will be on the look-out for B12 signs next time. If this is you, read this post; it might help! Good luck.