Why do I have duplicate songs in my iPhone?

I have about a half dozen Smart Playlists on my iPhone. For some reason, the same song will appear two or three times on my iPhone, but they are clearly only appearing once on the Smart Playlist on my iTunes on my computer. I reset the iPhone to its original factory settings, but the process was insanely complicated as it would not take the most recent back-up and I had to restore from about eight months ago. Now they are all appearing again in duplicate and I do NOT want to reset my phone form scratch every six weeks. Is there another workaround for this challenge?