At your age, lowbackache is common due to improper posture, prolonged sitting and wrong ways of bending forward.
Try the following:
*Hot water bag (10 minutes twice a day)
*After applying hot water bag, apply Nobel Gel
*Tab Flexon (1 tablet after lunch and 1 tablet after dinner for 7 days) (if you are not allergic to it)
*Tab Pantakind (40mg) (1 tablet before breakfast in the morning for 7 days)
*Tab Gabaneuron (300mg) (1 tablet at 7pm for 10 days) (this may cause some sleepiness for a couple of days)
*Lie down on your stomach, keep both your palms beside your shoulders, then push your hands so as to raise your head/neck/shoulders/upper body above the bed, then bring your head/neck/shoulders/upper body back down on the bed...repeat this for 40 counts (Bhujangasana) (don't do any other exercise apart from this)
*Avoid sitting on a stool/chair for more than 15 minutes at a stretch. After every 15 minutes get up for 1 minute and then sit again. This is very very important.
*Sit erect. This can be easily achieved by sitting on the edge of the chair/stool. Don't go behind towards the back support!
*While bending forward, make sure you fold your knees. Don't bend forward with your knees straight!
*Avoid sitting on soft sofas. Sit on hard surfaces.
*Avoid riding bike/car for a few days until your pain subsides.
Next Steps
Do let me know after one week to see if your pain has reduced.