Metformin can cause acidosis in some people. This takes time however. But one sign is tingling of the skin. It does not commonly cause itching.

If you have been on acid blockers for a long time, I think it would be a good idea to get your B12 checked. Acid blockers block absorption of B12. (other nutrients affected are folic acid, calcium, magnesium, iron, zinc)
Any number below 500 should be supplemented. (US ranges remain behind the times and quite low for normal). Many people with neuro problems are low in B12. When the serum levels get low, so does the spinal fluid concentration. Two conditions with proven low levels of spinal fluid B12 are fibromyalgia and MS, for example. But not everything has been studied yet.

Metformin inhibits B12 absorption too, as a side effect. So the longer you are on it, the likelihood of low levels developing increases. Normal people can have stores of B12 in the liver that can be as long as 5 years lasting. After those are gone, that is when symptoms start to show up. So if you have testing done in the past, reflecting using up those stores, after 5 yrs ( is a maximum optimum time) you may then test lower.