Hello, spine and back problems need a detailed assessment. Please get a formal evaluation done. However, looking at your symptoms and the degree of severity being assumed as mild, because you have described it as some back pain, you might benefit with back and abdominal exercises. But yes,  you need to consult a spine or an orthopedic surgeon for the  same before you proceed with the rehab program. Hope this helps

Get examined  properly by a doctor   before someone  can give you a diagnosis on messaging platforms

By looking at your history .... it looks muscle spasm... which is very common after sitting for long in one position

At this age very likely spondylosis / ligament sprain

Cause can be as trivial as sprain to disc. Needs evaluation. Consult for same thanks.

Bad posture is the most common cause.

It could be Lumbago.

Mostly improper posture and inadequate exercises leads to lumbar disc degeneration which could be the cause for this. Need more history for further management