Help putting on weight...

Hello. My friend and I are quite skinny people. Both 17yo, 125pounds, he is 5’7, i’m 5’6. We eat as much as we can (not on any diet, we eat junk). We seem to burn all of it very fast. both hyper-active, always need to be doing something. We don’t put on any weight at all. We exercise a bit, few weights a week, basketball at lunch, badminton weekends etc…

How to ‘grow sideways’ as we’re very light. Eat more carbohydrates? Fatty foods? heavish weights/low reps? I eat heaps of fruit/veg a day, and about 1.5-2 liters of water a day normally (50-70oz).

Any help would be appreciated.
thanks