Hey guys, I'm looking for quick advice about how to treat and manage a strained muscle. I've narrowed it down to my iliocostalis muscle only by what I've read online but I am going to a trusted PT to make sure I'm right. It hurts so damn bad!

I was deadlifting (450lbs) Friday and was tired from working all day. I could feel my lumbar not keeping form and I decided to push myself, welp! I felt the muscle pull with a sharp pain. I went to work the next two days because it wasn't too bad, I could at least function. But must have slept wrong Sunday night because I could barely move Monday and it's not better today (Tuesday).

I'd like a few quick tips how to treat it and how/when, to return training. The only movement I can do is the bench press at the moment. Thank you for the responses.