I had back surgery and i have a bruise on the right side and pain near the scar on my spine. what could be causing this?

Positioning : Bruising on your side may be due to the way your body was positioned during surgery. As far as scar pain? Is it red, draining etc. have surgeon take a look at it

Blood: Some degree of bleeding can occur following back surgery. When blood goes into the superficial soft tissues, it causes a bruise. Just make sure your surgeon is aware.