How come i can only hear through 1 head phone from my blackberry?

[koolest_kid_around]

So i take the train to school and all i have is my music/books. listening to music on this long train ride helps me kill time. now to my point, ever since last week my right head phone kept on cutting off sound, so i thought this was my headphones so i bought a new one. and that didnt solve the problem now only my left head phone plays sound and i dont know what to do, can some body please help me?