Tips On a Healthy Way of Gaining Weight {somebody help?}

Shy • Enjoying Life! Working going to school and Respecting those that Respect me!
Hello Everyone☺️ 
​    I'm a 28 year old That has been trying to gain weight since I was 20 years old. The highest I've been was 135. I've tried everything from BC, to GNC shakes. I have been stressing and I believe that is the total reason. Any advice on A Healthy Way for me to Gain Weight?
​I would really Appreciate it☺️