I'm currently going through the same thing. For background, I suffered a ruptured disc 3 years ago and had surgery for it - so I'm acutely aware of anything back related. Last week, after taking my son to the zoo, my lower back go progressively more sore throughout the day, to the point where I had difficulty sleeping that night. The lower back pain has gone away for the most part, but I've been left with tingling and numbness in my foot/calf. Only problem is, I also had feet issues from Xeloda, so it's difficult to differentiate between the causes.
From Jan-March, I received daily radiation treatments, which I can tell rather messed up everything located around my hips. Between that, and not doing much actual exercising, everything was tighter than a clam with lockjaw, which probably caused some injury to my lower back. I'm just hoping it's something that can be treated with time and PT, and not surgery again. Although, if I need surgery again, it'd be nice to fast track it and have it done while I'm recovering from my cancer surgery - I can't keep missing work due to my myriad health problems.
Long story short, be sure to stretch out all the hip related muscles. Sitting and inactivity shortens and tightens those muscles, putting a lot of pressure on the spine/lower back.
35yo male - father of 1 (infant)
Dx Stage IIIc - T3N2M0 8/15/18
8 bi weekly FOLFOX treatments done 12/11/18
1/23/19 - 3/1/2019 - Radiation + Xeloda (4,000 mg per day - 4 pills in morning and evening) - 28 days