It usually happens when you have lower back muscles weakness. Which as you explained because of your life style.
Next Steps
If it is too severe consult either a good physiotherapist nearby or a orthopedic doctor. But if it's not too much, than apply hot fomentation and little rubbing of your back muscle with pain killer gel, and lower back muscles strengthening exercises.
Health Tips
Avoid continously sitting, drink plenty of water, milk and increase fibres in diet. Avoid lifting/carrying heavy objects. Avoid forward bending with straight knees.