Problems synching music & playlists

My ipad wipes the playlists from iTunes on my iMac (rather than the other way around) every time I try and sync them.

When I tried to delete all the music from my iPad in iTunes, it automatically changes settings back mid-synch to my previous selection of music. Then when I manually delete music from my iPad, when I synch it wipes the playlists and music from my computer.

I've tried restarting my iPad, but I don't want to wipe the data/settings from the iPad as I don't want anything to go "missing". Both ipad and imac are all at the latest iOS7 - in fact, this problem started shortly after I upgraded.

How do I fix this? This is getting very irritating.