Music that I downloaded to iTunes off of a CD won't play anymore.

This happened two or three weeks after I got my iPhone 5S. Any music that I DIDN'T buy from iTunes will not play. The music still shows up on my Music app but it has a square inside a faded circle around it next to each individual song when it shows up on my phone. I have been looking for solutions for a month and I haven't been able to find anything that will help. Any ideas, anyone?