lower back pain

Hi ,

I had an L4/5 Discectomy and decompression of the left L5 nerve root on the 16/8/2002, since then have had on going back and leg pain. It has become worse since christmas 2008 and have of late been having a bad cramping feeling in my buttocks going down my legs resulting in my legs giving way. I also have bad pain if i sit or stan to long. Do you know what could be causing this to happen. I had another mri scan on the 12/01/2009 which said i had broad central disk bulge from my L3-L5S1 and mild spinal stenosis, my doctor said this was nothing to worry about could you give me some advice in what could be causing this and my pain. I am a full time mum of one who is fit and healthy i was a jockey up untill i had my daughter 2 years ago.

Thank you for your time