No matter what headphones I use or what I do to the settings the audio in my headphones will always go to one side (usually the left) after a few seconds and its impossible to change it back. Why is this a thing? I've found no one else online with a similar issue.

I assume you have tested with a known-good alternative set of headphones.

Does this also happen with internal speakers, if they are present, and with external ones?

Do you have pavucontrol (the Pulse Audio Mixer) installed? (It's in the repos.) Do its volume settings match the output you are receiving. You could try the Output Devices-->Lock Channels setting and see whether that makes a difference.

I have tried multiple sets of earphones, same result. I don't have any speakers. I installed pavucontrol and have tried to increase the volume on the lower side but it always goes back after a few seconds. I have tried to lock and unlock the channels. I have tried setting the volume in alsamixer.

Nothing works at all.

I'm not using Mint right now, but I have used it in the past and haven't encountered anything like this; indeed, I've never encountered anything like this.

Try booting to a live CD/USB of something not based on Ubuntu and testing whether it happens then. If it doesn't, then it's some really strange issue with your install. Otherwise, it might be some weird hardware issue the likes of which I've not heard of before. My instinct tells me that this is likely a hardware problem, but I have nothing specific to hang that on--that the relevant portion of the audio jack is losing contact after the initial connection.

If this is a desktop, you might try opening it up and checking the connections to the audio jacks.