How long are you sitting each day total?

Only 2-4 hours or so, but it aches after only a few minutes.

What kind of chair is it?

https://www.amazon.com/Black-Office-Chair-Computer-Adjustable/dp/B00FS3VJAO/ref=sr_1_10?crid=15WICUH2XY8BT&dchild=1&keywords=ergonomic+office+chair&qid=1613758497&sprefix=Ergono%21%2Caps%2C211&sr=8-10

Where does your back hurt?

Lower back