I don't know if this is a right place to start a thread but...
I don't know whats causing the problem and I might be sensitive about it but after variety of experiments such as hearing only one side for each, messing with the mixer, changed the Jack to new one, used it on MP3 player etc... I can confirm that left side is a little bit weaker than right side. Hence, I get to hear more right side than in the middle, where it suppose to be. Moreover, my friends tested the headphone and told me it was working perfectly where they can hear equally.
I've been using this headphone for nearly 10 month and haven't experienced this kind of problem before.
My only solution right now is to mess with the mixer so that I can hear on equal sides, or change the sound card for my PC which is kind of absurd IMO.
So if there is any solution for this problem, please tell me. I know that this issue is too broad to get definite answer but yeah... help would be appreciated it.
Oh, and another IMPORTANT note: I'm currently sick right now as I caught a flu so maybe my sickness caused me to hear less on my left side?? I heard that since nose and ears are connected to each other, it will affect the ears as well?? I don't know really lol