What Is The Difference Between Bladder And Kidney Infection?

Hi - what is the difference between a Bladder infection and a Kidney infection . Have extreme cramps in my lower abdomen. When I get the urge to go to the bathroom the pain intensifies ( in my lower abdomen) to the point I am hunched over - however there is no burning etc when I go. Started on Wed after swimming . I m a 64 year woman very active - also will drinking lots of water and Cranberry Juice help or even get rid of this. - Thanks Mary Lou