Iphone syncing unwanted songs?

I feel like my question is going to have a really simple answer, so please don't laugh at me. I try not to keep my phone bogged down with songs, so I keep only a select few on it at a time. To do this when syncing it to Itunes I have checked the little circle that says "selected songs and playlists" then click the box with the specific playlist I want. However, when I plug it into my computer to charge each night it keeps downloading songs I do not want and that I have not added to the playlist. I have looked everywhere I can think to and I don't have the songs or artists checked anywhere. I even removed all of my music and tried to recreate the playlist. It is a pain to have to keep manually deleting the songs each morning.

First of all stop automatic sync. That should stop itunes program from opening when a device is plugged in. You could use a wall charger if you have one which would eliminate all issue.