Hi i'm a 15 year old male, and I am really skinny.

This is going to sound weird but I need help gaining weight around my waist...
You see when ever I try to go shopping and buy me some jeans it never works out. This is because I never find jeans that fit me properly. Right now I wear jeans that are 28 inches for the waist and 34 for the length.(28x34)But that's not the proper size because I need jeans that are 26x34 which is completely impossible to find from any brand unless i get custom made jeans.

That's why I want to gain weight around my waist not fat of course not, but muscle which will be abs right? To get abs you need to lose fat which makes your waist SMALLER But that's not what I want so what do I do. I'm so confused and frustrated I really need help, but I don't get a lot of help since this situation is so rare and awkward.

I don't want to wear belts because then theirs a whole different problem, so what do I do?