What Causes Leg Numbness With Electric Shock Sensations?

I am 60 years old and have had two spinal fusions at 4-5 level. For the past five months I have been experiencing numbness in my legs and feet much worse on left side, but still evident in the right. In the past few weeks, my leg at the knee and just above is now burning like an electric shock burn when I stand for more that five minutes or so and a continual soreness when seated like the area has been slapped hard. Can you suggest a cause and a possible solution as I can no longer sleep with this pain and it is there all day?