What Does A Lump On Lower Back Indicate?

i have a knot in my back. my lower back, just above my waste. it bulges outward, so you can easily feel it with ones hand. it small sometimes and larger others. it is extremely painful ( 7 on a pain scale 1-10). it keeps me from walking correctly and bending. i hope this is enough info. thank you, Clint. ah yes i m 36