HELP - Songs are duplicated on iPhone but not in iTunes Library
I have duplicates of a few songs on my iPhone 4, yet on my iTunes Library (and music files on my computer) I don't have duplicates. I've noticed that the songs I have duplicates of are songs I have downloaded straight to my iPhone on iTunes. I have also noticed that because I have changed the genre of these songs I know have duplicates of them.
For example: I downloaded the song "Sexy and I Know It" and the Skrillex album "Bangarang" on iTunes on my phone. These downloaded successfully. Now, when I synced my phone on iTunes, and the songs appeared in my library I changed the genre of the songs because I like having them all in the correct places. So I changed the genre of "Sexy and I Know It" to R&B/Pop and the Skrillex album to Electronic. Once I synced my phone again, I have duplicates of the songs I recently downloaded. If I change the genres back to the default ones and sync again, the duplicates are gone. But I want to change the genres of the song and keep them because thats what I have. I know I can delete one of the copies by swiping and deleting on the phone but when I sync again it duplicates again, and I really don't want two of each song, it just doesn't look right.
So, the question is, how is it fixed? Is there a way to not have duplicates when changing the genres of the songs, because I believe that is the problem? The only thing I can think of is deleting them off my laptop and re-downloading them through my computer on iTunes? Can anyone help?
Windows 7