yep, highly likely that it is the cord. this is where earbuds with replaceable cords shine. the cord is almost always the first thing to go out (99% of the time), and generally one ear will go out before the other in these cases. I have replaced the cord on my tripleFi 10's 3 or 4 times now, in about 6 years. granted, I use them in the gym and whatnot.
edit: oh and to answer your question, its probably not something that you can fix. you'll probably need to buy a new pair (maybe one with a replaceable cord this time)