How to start a healthy diet?

I'm definitely bad about eating healthy I do make home cooked meals but I eat a lot of junk food too I'm only 94 lbs which changes from 90-97 I'm also 17 years old and 5'1 I'd like to gain weight like a couple pounds but I do that and my weight drops quickly I want to start eating more healthy but not to lose weight. I'm bad at exercising and get really lazy. I'm also very small and tiny 
Suggestions? I also would like to eliminate soy out of my diet or anything that's unhealthy in the first place