As Steev said, first check the wheel. You don't have to borrow another wheel, simply install your wheel reversed (cassette on left) and see if it moves closer to the other chainstay. If so, it needs to be re-dished to be centered on the axle.

Also, in case you don't do this yet, always mount your wheels with the bike vertical on the ground and let the wheel find it's natural position. Mounting off the ground risks mounting with the wheel not fully seated on the dropout.

There are two other tests for a wheel problem.

Check that the axle exrending beyond the face of the nut is cylindrical (threads are OK if not mashed too much), extends at least 3mm and doesn't have anything on it like the QR spring. Next check for a bent axle by standing the bike up with the QR open, rotate the axle and watch for movement of the rim between the stays. If there is any, you have a bent axle.

Now if the wheel tests 100% OK, the problem is in the frame.

Either the rear triangle is bent to one side. Or one dropout is slightly forward of the other. Step one: with someone holding the bike up and the QR open gently push both ends of the axle forward in the dropouts so they touch the forward face. This is important because that's where the wheel will go (at least on the right) because of chain tension. If that solves the problem, use some body filler on the backs of the dropouts so the wheel always goes there.

If it's still off, use a rat tail file to file away from the front face of the dropout on the side where the wheel is closer to the chainstay, and test again. Work slowly and keep checking because the rim will move roughly 5 times the amount you file away. If you shape the top of the dropout carefully you can make sort of a wedge so the wheel always find home, but be careful not to change the vertical plane of the wheel.

Lastly, and before filing, or filling check how the wheel centers with respect to the seat tube. This is more meaningful than centering in the stays. Mount the wheel in the natural position, and lay a straight edge across the down and seat tubes extending out to the rim. Measure to the rim. Repeat on the other side, at the exact same place on the tubes (this is important so use a good reference). The distance should be the same.

That's it, and unless you crashed, I expect that you'll find it's something simple like the QR spring on the axle since it used to be right until now.