Weight “problems”

I’m 18, I weigh 50 kgs and have been this weight for six years now... no matter what I eat I stay the same weight.

I started going to the gym for some years and eating big meals to try gain weight as I am unhappy with my body... I want to gain at least a little more weight I’m really unconscious about it... what do I do? How do I put on weight when I’ve literally tried eating more , let alone I am already a pretty big eater, and I gym with weights and do no cardio??