Dude. there is no real mass gain without some testo. This days you can do it with help from a doctor even. You can go to a sports doctor or to an endocrinologist, is easy to get some scientific adivise, and do the stuff in the healthiest way. You can go to a nutrologist as well to find high callory food, like avocado for example, you can eat a lot and don't feel full, it has a lot of calories, some carbs and good fat.