It’s most likely sitting at work for such extended amounts each day has your hip flexors tightening up. When hip flexors get tight (they’re at the top of my quads connecting to the hips) they cause the hips to tilt due to the extra pull the tightened hip flexors are exerting.

Due to the hips tilting, the lower back had to work harder to compensate, and over time it causes the lower back muscles to get angry, tight, painful, and can even have muscle spasms.

I’ve dealt with this for years, the solution for me is hip flexor stretches, and using a roller to roll out the tight hip flexors. I’ve experienced the beginnings of discomfort in my lower back, then start using a "sprinter stick’ to get the hip flexors to relax by rolling them, plus stretches, then my back pain starts going away.

I too work in a office, I also sit and game a lot too, so this has been a problem for me for years. It wasn’t until the last year did I get told what the real problem was, and now that I have a solution, I’m happy to share that with you.

Also everyone else suggesting exercise aren’t wrong, I know it sucks, but exercise helps a ton of other things too, so it’s worth considering, even if it’s just long walks at first. If you have any follow up questions, please don’t hesitate to ask!