It is a very long slow process to put on weight. Try avocado - 1/3 to 1/2 per day. Nuts are good sources of good calories as well. I splurge and have dark chocolate covered nuts sometimes. I also have dark chocolate daily. I will have some “ice cream” made out of cashew milk and sorbet. Eat lots of small meals. I also eat chips and salsa. It’s hard as I eat nothing fried and very little added sugar in my foods. It will take over a year to start putting on the weight, but don’t be discouraged. I also do not drink alcohol so there are no calories there either.