Q: always restoring

I have the ipod touch that I bought from the Apple store online in September of 2014. I like to manage my music manually, as I have been with my previous ipod classic's that I've had. The problem seems to be that after I plug my touch ipod into iTunes for an software update, I always get a message saying my ipod will have to be restored to factory settings.... and so I do the factory restore, and lose all the music I put into it.

I use this ipod on two different Windows' pc's. I listen to the Sirius app on it everyday. Is there something, that I'm doing, that is causing me to have to restore this every two or three months. I just don't want to get another one, and then the same thing happens. I just want it to keep all the music manually put into it, as with the ipod classic.