I Have A Very Sharp And Deep Pain Located In

i have a very sharp and deep pain located in the lower middle of my back 1/3 of the way up from my belt line to my neck , on the right side of my spine about 1 1/2 to 2 inches right of the center of my spine. it started very fast about a week ago after riding on a lawn mower racking leaves with the leaf sweeper. no physical strains at all. what can this be? it appears to get better when i stay sitting and when my bladder is full. when i stand up the pain is very severe and as i pee it gets worse as my bladder empties. any ideas?