Noise from crankshaft spindle and pedal falls off

[mm391]

Hi,

IN the last 6 months I have been getting really bad noises, creeks, clunks etc coming from somewhere around the spindle connecting to the crankshaft. Every time I put pressure down on the left hand pedal, either it or the spindle attaching to the peddle creeks, clunks real loud and the the pedal works itself loose. I have tightened it up every time and after a couple f days it becomes loose and almost falls off again. Can anyone help explain why and how I may fix it myself?

Thanks

MM