I expect OP will find that herniated disc(s) in the lumbar spine are the cause.

I suffered rather persistent and painful sciatica for years. My Primary at the time, a great doc in every way except one. He did not like to refer to specialists. Doc 1 left the practice, I got a new Primary. First visit, he sent me to either an Ortho doc or Neurology, been too long to remember.

MRI shows herniated discs at L5-S1 and L4-5. I was 35 at the time and the news crushed me. Seriously I felt like my active, athletic lifestyle had just been stolen from me.

What helped? Terrific Physical Therapists and a double-crap-load of PT.
I usually stay on top of it with stretching and CORE STRENGTH!

See a doc, get the MRI, get diagnosed and GET AFTER IT.

Luck,
fat biker

P.S. This is no miracle cure. I takes effort and time. I take Naproxen 2/day.