Hi, I Am A 21 Year Old Female Who Has

hi, I am a 21 year old female who has been struggling with weight gain since i was about 6. i was always skinny and small, always having my ribs show and my legs looking boney. I eat 2-3 meals a day with about 2 snack in between but i still do not gain weight.sometimes i feel like i loose weight rather than gaining it . I've talked to doctors before, and they always tell me to just eat more. i always feel full really fast and sometimes i have to force my self to go and eat something. i only weight 84 pounds. I want to do something about my weight because i do not want to risk any health problems down the road. do you recommend any type of medicine that could help me ?