can you suggest me a vitamins to gain weight?

What is the vitamin to gain weight 
Weight gain is mainly dermined by the healthy diet that should include protein, fat and carbohydrates that meet your daily requirement in addition supplemental herbals could be used to enhance weight gain like saw palmento seeds and mexican wild yam root, vitamins include Vit D 50000 IU once weekly and iron supp. consult a dietrititian for further workup
investigations 
After proper physical exam, cbc should be done to look for anemia, Vit D and calcium should be done to look for signs of hypocalcemia, Total protein , Albumin, and pre Albumin should be done 
Causes 
Genetic/ Familial
Intentional weight loss 
malabsorbtive disease 
Our advice 
Try to have well balanced diet