Lyric discussion by Status 

Cover art for Jellybelly lyrics by Smashing Pumpkins, The

I've always thought this song was about the grunge movement. The first verse reminds me a lot of an old U2 lyric: "I don't believe in the 60's in the golden age of pop You glorify the past when the future dries up". I think the song is satirizing the state of music back in the early 90's where bands like Bush and Candlebox were popping up all over the place.

"down in the belly of the beast" is key to the second verse. The Beast is traditionally a supremely evil figure in religious myth (specifically Satan or Hades spring to mind), but "The Beast" is also slang in some circles for the media, which is what I think Billy was leaning towards here. It's not just that he's "so sick", it's a level of disgust with his surroundings (which I say is the media).