Piriformis syndrome?

I have just been diagnosed with this. I have had sciatic pain in the left leg for 4 years now. The pain is most severe down the outside of ankle. Sitting bothers this leg most. If I stand for more that a half hour the pain soon becomes severe in the left leg. On the right I have developed pain in the buttocks accompanied with spasms of the hamstrings when trying to straighten the leg after it has been bent for a while. I also have a painless sensation that shoots down the length of the right leg that momentarily weakens the leg to the point that when I am walking I am not sure it will support my weight. The pain in the buttocks is bad while trying to bring the right leg forward while walking and with the left foot on the heel of right shoe it is very painful trying to pull the right foot out of the shoe. An MRI showed nothing remarkable, small herniations at L4,5-S1. I would appreciate any help. Thanks