Hi zorrro13 & welcome to this forum, usually excessive alcohol use causes huge depletions of B1 levels out of the body, so especially the thiamine supplements are a very good idea, i took 3 x 100 mg daily of B1 for a long time, it seemed to help some with the burning, for me anyway, with the B12 methylcobalamin normally 1000 mcg [on a empty stomach] daily is the least we take here, some here take 5 mg [5,000 mcg] daily, depends on the individual & of course the other B vitamins in a multi B are needed as well to help the other B's work properly.
Have you had a Glucose Tolerance test or just the fasting Glucose test ? as a fasting glucose test is useless for testing for Prediabetes, which can cause the same nerve problems as a full blown diabetic.

good luck with the neuro appointment anyway.
Brian