I have read the complete details in your question.I am unable to know from your details about your age.
It looks that you have old history of injury
at your back & your MRI
is showing prolapsed disc at level of L4 5 S1,2.This may be the most probable reason for your symptoms.Injury to your back may rupture the protective covering of your disc & internal disc material may protrude out & compress the nerves coming out of the vertebrae.
You should consult to a orthopedic surgeon in your area for this.Depending on clinical examination & your age you may be prescribed some medicines combined with exercises or he may advice you for surgery.
Hope this will help you.