I have been facing backache from many years I don’t know what exactly is paining As per my research I think it’s the sacrum in my back bones which is almost near the pelvic bone on left If I sit for long it’s painful plus the backache in winters troubles me a lot. I exactly don’t know the terminology for the body part but it’s the end of my spinal cord probably in the left side of my body . Plus I am overweight too but when I had a controlled weight during that time also I faced this pain