What Causes Constant Pain In The Left Side Of Back And Abdomen?

For the past week I have been getting this terrible constant pain in the left side of my back which spreads to my side and abdomen. The pain is very sharp at times and increases when my bladder is full. I empty my bladder to feel another sharp pain in my left back - it feels like a release but is very painful. I have also found I ll go back to empty my bladder within 20 minutes of going the first time. It does not sting when I wee - I have had UTI and a kidney infection years before and know what those feel like and I can say this is a pain I haven t felt before. I was diagnosed with flabby kidneys in 2012 (I think she said it was my left one and she said they never went back to their normally shape I am really worried about this pain because it has been going on for a little while. Thank you