Lower back pain from 6 months.

I went to doctor and suggested for excerices, I did it regularly, my weight is 70 and athletic body, did IFT and physiotherapy and got some relief but after that I continued excerices as well but still pain persists, I have sitting work almost for 9 hours and in middle I stretch my lower back as well, sometime pain radiates to hip and legs as well but not much, while sitting and walking I don't feel pain and I feel more comfortable but when I stretch lower back from both sides I feel pain. I am using hot bag, I am using more stairs to climb up and walking more, in middle I felt less pain but it's constant. When I wake up obviously it's more pain. But in day to day activity I don't feel pain or very less. Should I avoid stairs ? I do normal walking, but no benefit. Any suggestion ?