being an ocd suffer myself for years and reading lots of other peoples posts stories over the years it seems a large majority of ocd sufferers at some time in their life fear they may be schizophrenic. trust me, ive been there myself. also, i have a song stuck in my head all the time. currently it is the song "all of me" by john legend. it is a symptom of ocd but they actually have a name for this and its called "earworm" there have been books and studies on this.
this following part is from a wiki post: "In a 2006 book by Daniel Levitin entitled This Is Your Brain on Music: The Science of a Human Obsession, he states that research has shown musicians and people with obsessive–compulsive disorder (OCD) are more likely to suffer from earworm attacks. An attack usually involves a small portion of a song, a hook, equal to or less than the capacity of one's auditory short-term memory. Levitin reports that capacity as usually 15 to 30 seconds. Simple tunes are more likely to get stuck than complex pieces of music. He also mentions that in some situations, OCD medications have been known to minimize the effects. In 2010, published data in the British Journal of Psychology directly addressed the subject, and its results support earlier claims that earworms are usually 15 to 30 seconds in length"
but even people who dont have ocd can get an earworm.