Diagnosed w/ small bowel bacteria overgrowth and carb intolerance (secondary). what could cause each?

They are related: Sibo or small intestine bacterial overgrowth is a result of a multitude of things, det included. Carbohydrates, including fruits and grains feed the bacteria in the gut and causing the bacteria to grow in abundance. This then interferes with the digestive process and this leads to fermentation of certain foods (carbs)- causing gas, bloating, etc. Seek a functional medicine md to "heal your gut".