Gaining weight is simple; simply take more calories than you burn. I'll assume that you train everyday for softball and on a weightlifting program. What I can say is that you should eat more than you want to eat. But eat clean and healthy foods, not junk.

Stuff like red meat, meat, cheese, veggies, fruits. If you are really struggling to gain weight, add olive oil and peanut butter to your diet.

Victor Roffel blog