Hi
If it is solely low back pain not causing any travelling pain to your legs then it could be mostly due to weak muscles and bad posture.
Keep a small cushion behind your upper or middle back while sitting, this will prevent forward slouching and will give support to your back.
You need to start with :
> Mobility exercises for back muscles.
> core strengthening exercises.
> postural correction
Next Steps
You can keep hot water bag on your lower back for 15 mins to relax your muscles.
Health Tips
Take a break from sitting in every 1-2 hours, move around , stretch your body then sit again.