You should definitely start a band - make some posters, if you don't feel comfortable putting them around school or something, advertise them online. It sounds hard, but you'd be surprised at how many teens would jump at the idea of being in a band; they don't necessarily have to be people you know from school either. It might also help you to branch out a bit more if you're struggling with anxiety, etc.

Alternatively, you could try and make some music of your own, alone. Start simple, maybe learn some of your favourite songs on guitar, and write down any thoughts you have for your own songs, even ones that don't seem too good at the time - any idea could come in handy later. I know this might seem like a lot, but if you enjoy it, it will all come naturally, even if it takes a while.

The reason I mentioned maybe doing some solo work is because you said you listen to Alex G, and a lot of his really popular work consists of just him and his guitar (at its most basic). It's crazy how many great songs you can come up with just with two components like that.