duplicate songs on iphone not itunes

I ripped a CD into iTunes, and then put it on my iPhone 5. After doing this, my phone now shows duplicate songs for all of my music, not just the newly ripped CDs. My PC is old and has a small hard drive, so when I rip a CD, I transfer it to my iPhone and then delete it from the computer. That's why this is so strange; it's showing duplicate songs after syncing, even though those songs are no longer on my computer. Deleting the duplicates on the phone deletes the original song too. The help hotline and genius bar were both unable to find the cause or a solution. Anyone have any idea how to delete the duplicates without reloading all 2800 songs to my phone?