Need help Gaining weight

paige
Can anyone help me gain weight. Im 20 years old and im really under weight for my age. Im supposed to weigh 150 but i weigh 103. I was 150 at one point but i lost weight cause i was in a bad place and no job. So i want my old weight back. But i honestly dont know how i can gain it. My weight i have now is scaring my fieance.