Girls, how do I know if it's my back or kidneys hurting? I was sitting…

Girls, how do I know if it's my back or kidneys hurting? I was sitting half-lying down, felt like breathing became hard... I've been lying down for 20 minutes on my side, as if someone is turning my lower back... The urine analysis that month was good, I had pyelonephritis before, I worry How can I tell, maybe not the kidneys but the lower back? Thank you