I want to gain weight quickly, can you help me?

I am 18 years old, 163 cm tall (5' 4") and I only weight 47 kilograms ( 104 pounds) and I am a little overweight. I want to gain 3 kilograms( 7 pounds) in a short amount of time( preferably about 1-3 months) I used to have gastroesophageal reflux disease (GERD) because I used to eat rarely or even not to eat at all, some days, and when I ate, I ate food that was rich in fats. I had horrible pain and it was very hard for me to eat, very cynical because if I didn't eat, it was going to be worse. I barely could talk.I used to have a normal weight a few years ago but now it's getting harder and harder to gain weight. Please, help me.