Back pain at this age is commonly due to bad posture, spine muscle weakness, prolonged duration of work in same posture. Consult an orthopaedician to rule out any spine abnormality. If it is postural problem, you need to learn spine muscle strengthening exercises from physiotherapist. Mainly focus on strengthening of lumbar core muscles (transversus abdominus, multifidus) which are required for posture and stability of spine. If other spine muscles are also weak, you will need to strengthen them as well. Physiotherapist can also guide you about how to correct and maintain good posture.
Next Steps
Take break in between work (preferably a 5 minute break every 2 hours). Avoid lifting heavy objects or carrying heavy bags till your spine muscle strength improves.
Health Tips
The following article has information on work ergonomics:
https://www.practo.com/healthfeed/workplace-ergonomics-to-prevent-back-pain-24396/post