Synching iPod with computer

Every time I plug my iPod into the windows computer I lose my playlists. I don't lose any music that I bought from iTunes but I have lost other music. Why do I lose my playlists? What a pain to regroup albums and other playlists. Anyone have an idea? I would appreciate it. iPod touch 4th gen. It has always been a problem since the beginning. My software has always been up to date. So I am afraid to plug into my computer to update iTunes or whatever reason because ill lose my playlists. What a PITA.