Audio only playing on one side

So it's nothing to do with the camera/audio equipment. The audio picked up on both sides when reviewing the footage with earphones, and Premier picked up the same when putting it onto the timeline. But after working on my edit for a bit without my earphones and then later coming back to review it with earphones in, it's only playing on the left side. It's not to do with my earphones either, as it plays audio on other sites just fine, so this problem is only specific to Premier. What's also strange is that my footage from the uploaded media storage is also just playing on the left now, so I doubt it has anything to do with a particular effect I added to an audio clip.

Any suggestions?