'Bellyache' is totally fictional. I like writing about things that aren't real. The song is about not trusting anyone and then putting trust in yourself and realizing that you don't know what you are doing, either. Or realizing that things you do with a group of people that you think are cool in the moment are ultimately all on you.

I play piano and ukulele, and I taught myself those things just because I wanted to play them.

I've always been a singer. I never really decided I was gonna be a singer. It just kind of - I just sung a lot.

Billie Eilish Quotes