Headphones sound laptop only on one side?

I have a problem with my sound. No matter which headphones I use, I can only hear the sound on the right side. It's not always like that, but sometimes it's just like that. For example yesterday it went on both sides, and today it only works on the right side, that's pretty annoying, does anyone have any idea why this could be and possibly a solution for me on how to fix it.

Loose contact? Check all connections.

It's not because of loose contact, I've already checked everything, so it's pretty strange, and questionable why the whole thing is.

Then the sound card has a defective one.