Music doesn't sync to iPhone 5

A couple of weeks ago everything was fine, however the songs I buy from iTunes and the ones I download seperately do not sync to my iphone 5.I can play the songs on my itunes library however when I connect my iphone there are these weird circles next to some songs which do not sync. I attached a photo of my library just to make everything clear.The ones which have a circle next to them do not syncWhat does the circle mean? How can I fix it? Need help ASAP.Thanks