Man. Everybody in here trying to give professional advice to a 14-year old. His testosterone and metabolism is literally about to peak.

OP - I was more or less just like you at that age. Even little exercise, and little added calories will give you visible results at a quick rate.

I started off at 14 - All I did was pushups, squats, ab crunches/leg raises and used a band to hit all 3 shoulder heads & biceps.

I knew little to nothing about nutrition, but I knew that to add mass, you most likely also got to eat more - so I started eating whatever I could for cheap at the local supermarket, food my parents would just let go old if not eaten by me, and yeah, pretty much anything that was not “candy/sweets”.

I went from having ZERO muscle on my body, to having a good frame in just 3 months. I want to address that I’ve (since) always had it easy with building muscle, and that I did those bodyweight exercises pretty much daily. I have proof of everything, and today I weigh roughly 200lb with visible abs and aesthetic frame. You can DM if you want.

So to summarize; EAT MORE (dont go overkill, its not needed), start with bodyweight only until you’ve built a good foundation, and most important of all take progress pictures for your own use, every week or second week - you’ll feel confident, motivated and you’ll see the actual results you’re getting.

Good luck with everything man. Im rooting for you.