it's not tht a noobish question as the title suggests, at least i hope so

My wav-file sounds as it should mixing-wise, so the kick and the bass and the vocals are all set to my taste, but when i convert it to a 320 mp3 using audacity the whole mixdown sounds like shit to me.
No kick at all anymore, the vocals are drowned out and almost not noticeable, whereas pads and melodies are far too much in the foreground.
As stated above i use audacity and wanna convert it from wav to 320 mp3.
hope u can help, thx a lot,
Tordal.