I put two pillows under both my legs which rolls me a bit more onto my back (still on my side though) if that makes sense. The duvet is tucked behind me up my back and that's stopped my back hurting. Whenever I don't do that it hurts
You may have to have the added support from now on. I would recommend going to see a chiropractor as well or look on YouTube for physical therapy exercises for low back pain and do those.
This is the channel I follow https://youtube.com/@toneandtighten?si=BRGCtci6QVgXqKEu
Put a small pillow between your knees. May need some low back support.