been sleeping on my left side with pillow in between my legs but woke up feel backache every mornin

I bought maternity pillow from Shopee. Here's the link: https://shopee.sg/product/96953349/1619976151?smtt=0.262283135-1665972327.9 You can change position, laying flat or left side. I dont sleep on the right side as it is very painful and uncomfortable.