This has never happened to me before, and I started panicking that I forgot to throw something out or something like that. Then I realized it was coming from the pipes. What could be the issue?

Maybe they’re clogged. Honestly, it’s hard to say when all the info you’ve got is just “there’s a smell in the bathroom.” Call a plumber and have them check everything out.

Honestly, it could just be that a pipe’s clogged, or something got stuck in there, or the sewage line is blocked, and that’s where the smell is coming from. I agree it’s best to call in the pros, and if you’re in Seattle, I recommend these guys https://bens.plumbing/services/drain-cl ... o-jetting/ , who I always use. I like that they only use modern methods and tools for cleaning.