For reals though, drink a quart of milk a day. It's easy to do and that's about 400 calories right there. Snack between meals. Nature Valley Granola Bars are between 150-200 calories each. Two of those a day is about 300 calories on the conservative end. On the low side, you just added 700 calories a day to your diet. That's 4,900 calories a week, and 137,200 calories in a 28-day month.
That's just one example. Bananas, nuts, a potato every now and again, there are so many calorie rich, easy to eat foods to help you gain weight that are actually good for you.
People will be all like "Bro, eat a burger. Eat a twinkie. Drink a Coke." DON'T! Shit is high in calories and you get nothing healthy out of them to help you out. In fact, they could make things worse. You can literally be underweight and still have high cholesterol and shit.
You're still looking good. I'm rooting for you. I appreciate you. Keep pulling man. You can do it.