How can i get my appetite back ?

Well I have always been a pretty small girl 21 years old , 5'3 115 lbs normally , About 2 months ago I had surgery and i was put on Percocets . I have been off them for a month now , and still my appetite is still gone . I weigh 102 lbs right now , and don't think i am anorexic because i don't have body image issues and i actually want to gain weight . I usually only want to snack on really sweet foods , which dont have any of the nutrition I need . I Usually eat a meal a day and 2 pretty good snacks ( like a pop tart for breakfast and a slice of pizza for lunch and then dinner) But i have a very physical job and burn ALOT of calories . I am just looking for tips that will help me be able to eat as much as an adult should . thanks