How can i gain weight?

I'm almost 18 years old, I'm 5'2 and have never weighed over 100 pounds, ive tried eating more calories a day but that just gets me sick. i currently weigh 94 pounds id like to gain 10-20 more, i am considering birth control but im not sure what to do. my cousin took a birth control that helped her gain 20 pounds. should i try that?