Earphone sounds are backwards

Sounds in the game coming from the right side go into the left side of my earphones and vice versa. It's confusing because I can't tell what direction gunshots are coming from. My headphones are connected to a headphone jack on my computer monitor.

switch which ears the headphones go on.

It maybe on "Reverse Stereo" in your sound setings 'if' it has one,What is your sound card?

I hate to suggest the obvious, but... are you actually, y'know, putting the earphone marked 'L' in your left ear and the one marked 'R' in your right ear?

Most sound card control panels have a 'Flip Stereo' or 'Reverse Stereo' option. Give that a go.