OK, I just figured out that for DOOM 1, you have to name each song you put in the music folder after what level it plays in, like "e1m1, e1m2, e1m3, etc.) Do you do the same thing for DOOM II? Like "map01, map02, map03, etc."?

Music filename must match music lump name in WAD. Open WAD file, check how music lump is named and name your song correspondingly.