1. Get tested.I'm ok-ish, got the flu, then my back went out on me. Because of that I wasn't able to work on the house at all last week, and likely won't get anything done this week either.
2. Ice packs for 36 hours, then alternate ice and heating pad. Let it recover. If you can find a fascial tissue stretch therapist that will work wonders for recovery and determining why it went out and what you need to do about it. If you have to stress it and it lower back area, this is a very good support that you can wear under your clothes: https://www.serola.net/product/serola-sacroiliac-belt/
3. Hope you feel better soon.