In my youth I can remember having much the same problem, but not to the extent you seem to have, and it didn't last that long. But portable music was not available then, unfortunately or fortunately ...
Listening to a source of white noise might help, that is, like the sound you get when listening to older analogue radios when not tuned properly to the actual radio station. This should at least mask the music, and gradually lowering the volume over time might do the trick. It will need some experimentation but might at least allow you to concentrate on other things. It seems that an app exists for the iPhone, and there will probably be white noise generators available, but an alternative will be a small minature radio, as long as it is analogue rather than digital, since often the latter screen out any hiss. I'm sure that if you explained your problem to college staff, they would understand and let you use any device you saw fit to use. Perhaps worth a try.
http://www.nytimes.com/2011/07/07/garde ... .html?_r=0A longer term solution might be in doing some singing or learning to play an instrument, since this, like the anagram approach (link below) might divert attention away from internal listening. Going for long walks in quiet surroundings might also be helpful, as might be any physical activity that requires your full attention.
http://www.telegraph.co.uk/science/scie ... worms.htmlFor many, this problem just goes away eventually, but it seems it can last for much longer periods. I hope it is the former in your case. Good luck.