My lower right back hurts a lot. I'm not sure what I did

Go see a doctor then read anything by Stuart McGill

Are you squatting or deadlifting by any chance?

>>42814069
Most acute low back pain resolves on its own, although don't freak out if it comes back occasionally.
General advice is to stay active but avoid specific activities that seem to aggravate the pain. In other words, keep going to the gym, but don't do exercises that piss off your back (gradually reintroduce those exercises at a later date).

If you can't feel anything in your crotch and/or you're shitting yourself, see a doctor immediately. Otherwise, keep calm and carry on.