Back massage - if you can get one of those massagers that you put in a chair it’ll help so much! After my 3rd kiddo I kept throwing my back out over and over and over again. used the massage chair 3-4 times a day, heat pack, ice (rotate the 2), ibuprofen, and when he starts to feel better, core strengthening exercises. Unfortunately once you throw it out, it can keep happening. It’s terrible. I hope he gets better soon!