What Causes Muscle Spasms In Hamstring And Gluteal Area?

I am 56 yr old female. i was diagnosed with a narrowed L5-S1 disc at least 25 years ago. On and off I have had sciatica mainly in the buttock area. Lately I have been having muscle spasms in my hamstring but also in the gluteal area. I have also had a bulging disc at C-5 and last year a bulging disc at T5. I also have stiffness in the low back.