Hi
I have exactly the same problem, and I really believe that it is a common problem among the Earpods based on the number of complaints that I've seen.
I also use an iPhone 4S with my Earpods. I bought my first pair in late 2012 and the right side lost all its sound around 7 months later. I took it into the store where I bought it and they sent it in for analysis and it was determined that there was a manufacturing problem (AKA not as a result of my usage) and they were replaced.
However, the new set of Earpods only came with a 3 month warranty as opposed to the 12 month warranty you get with a new Apple product. Lo and behold, after about 5 months of use, the right side died just the same as the previous set.
It's not earwax or debris as I clean them out regularly, and you can hear the piece getting softer and softer until it eventually stops working.
This is pretty frustrating as I'm also a massive Apple fan and it just disappoints me that products of theirs can fail like this.