There are many solutions from a setting in the driver to a cable. Pick which works for you.
So I've had my computer for about 7 months now, and have never really noticed this problem until a couple of weeks ago. When I play games, left sound comes out my right headphone and right sound comes out my left headphone. And I thought it was a bit weird sometimes, because I'd hear someone creeping up on me to my right but when I looked I'd die from the left. I was very confused for quite some time. Then it hit me: the sound is reversed. I searched online for some answers, but found none other than "turn your headphones around" (but they have a mic attached so that wouldn't work) or "update your drivers". I have tried updating my drivers, but all are up to date. If it helps, here's my specs:
Motherboard: MSI 970A-G43
CPU: AMD FX-8320 Octo-Core
Memory: 8GB DDR3
GPU: NVIDIA GeForce GTX 950
And I built the computer myself.
Any help would be greatly appreciated!