How do I find which iTunes Library I am synced to?

I have three computers (all Macs) that I use at home, school, and work, but I can't find which library I am synced to. I have connected my phone to all three and tried syncing my music to my iPhone 5, but all of them keep asking me to delete my music, movies, TV shows, etc; I don't want to lose any of the music that I have on my phone, because apparently I have 200 more songs on my phone than I do in my largest library. I have some old CDs that I want to import to my library and phone, but if I can't find out which library my phone is synced to then what is the point?