Vitamin B12 deficiency?

I went and bought a spray of B12 from the health shop works wonders gives me some energy

Hi @maiti, Googling side-effects for Metformin you are correct. Metformin is reported to lead to B12 deficiency. I could not find any information about why this happens.
But sites like mayoclinic.com provide other causes for low B12, such as an auto-immune condition, pernicious anaemia or malabsorption of B12 such as in coeliac disease. (diabetes is an autoimmune condition in some of us, where the body's own immune system attacks a particular tissue or tissues in the body and this causes symptoms).
Your doctor can order a test to check your B 12 level.
Why start on B12 spray or whatever until you have a test on which to base a decision?

Ask you doctor for a blood test. B12 deficiency’s not uncommon on Metformin. I had it and now take a supplement each day as prescribed.

Totally agree with above.
Not sure that brown spots on lips are a sign of B12 deficiency, so if bothered about the spots, I would ask your GP.
As above, if your B12 level is not known, GP can measure it.
B12 deficiency is very common as folk age ; I am not sure of your age, but less common under 50-60ish years, and not sure if you are on metformin.
Best wishes

A vegan diet could cause B12 deficiency!

It’s also is hereditary. I have had problems since my 20’s as has my mother and her sister.
For some their body just doesn’t absorb it well.