Hey there! "The exact problem is that the muscles get tired doing the same job and when tired, They don't want to do other job."
You must relax your muscles and change activity during work hours at some intervals. Do in-chair cat and cow stretch exercise and in-chair twisting of torso in midst of working hours at some time intervals.
In morning, Do full body stretch 10 times, cat and cow stretch 15 times, bridging with hold 8 times, bhujangasana 8 times, and maintain sphinx pose for 10 seconds 5 times.
After work, in evening, Take bath, do hot water fomentation over back, and then do cat and cow exercise 10 times and bhujangasana 5 times and sleep.
While doing work maintain mostly proper upright posture.
Next Steps
The above specified plan should fix your problem. Do it in pain free ranges i.e. stop doing when pain arises.
Health Tips
please feel free to consult online in case of doubts.