iphone 5c reinstalling music after sync

Hopefully someone will be able to help as this has happened for the third time. I have ios 8.1 on my iPhone. I go to import a cd into my iTunes library that's fine, I am on the my iPhone screen in my itunes (artists, albums etc, I like to sync via albums rather than genre or artists) I make sure there is a tick next to the new album I imported & click sync. It doesn't sync on my iPhone. I try again and it decides to re copy my entire music library to my iPhone.What the **** am I doing wrong?! Ever since the last ios update it has done this.It takes over 4 hours to get everything back on.I am at the end of my rope.Thanks for your help.

I can't say for sure what's happening without looking over your shoulder, but make sure under options for your iPhone (when it shows up under devices in iTunes) that you have placed a check in the box that says: "Manually manage music and videos". Also check the box thats "Sync only checked songs and videos".