What Causes Kidney Pain Post Injury?

I have had left kidney pain for 2-3 days. I didnt start until I fell helping a friend move some items in her house. That same night is when it begin and only on the left side. I ve had kidney issues before and i m not surprised but I have trien flushing my kidneys with water and cranberry juice(low sugar). Some relief but still achy, pulsating pain from time to time. Is it real serious?