Gaining weight

Okay so all of my life, I've been skinny. While I didn't necessarily hate my body, I disliked it sometimes when certain clothes wouldn't fit how I felt they should've. My sophomore year of high school (when I started having sex with my bf) I went from 100 pounds to around 115. Through the years, I was depressed and lost some weight but never thought anything of it as I had always been skinny. I stayed at 105 pounds since 2011/20/12 until a few days ago when I weighed myself and saw that I only gained 2 pounds. I realize now that of course I'm not the only one who has this struggle of gaining weight... But I'm wondering has anyone gone through this? Has anyone had success in gaining weight? Can you share what you did to gain weight? Thanks in advance!