Yes, after 12 years of gastric bypass, deficiencies of minerals, vitamins and trace
elements may develop and cause poly-neuropathy. If vitamin B12 is ok then vitamin B6, folic acid, vitamin D, electrolytes and blood glucose levels should be checked. Also, effort should be made to look into the possibility of cholesterol, albumin and thyroid disorder.
After you opt for these tests, you can take a multi-vitamin supplement with zinc and magnesium, iron, multivitamins including B12 and B6.