This is how I started to gain weight. Take methylfolate. Have you looked into the MTHFR gene? You may have it which means you are not absorbing B6, B9, or B12 efficiently. Try taking the methyl forms of those supplements and this will help you gain weight. It worked for me. Took me 36 years to figure this out! I also went gluten free and I am on a Nutritional Balancing Science program.