My music sounds "empty"

Lately I've realized that my music sounds "empty" and "dull". For example I'd try to get a simple groove going with drum, bass, guitar, and maybe a synth... and it just ends up sounding flat. Other songs I hear sound so full, and lively even with very minimal instrumentation (drum, bass, 1 guitar). I keep trying to fill in this "emptiness" by adding bunch of reverb, EQ , doubling melodies, distortion but in the end they just make the song sound messy and it doesn't solve the problem...

What do you think is the biggest thing thats causing this? maybe bad mixing?