do you sleep enough? get at least 6 hours of sleep if you're sleeping less than that currently. if you sleep/study with your belley facing down or curve your back while sitting, quit it asap. It causes deformation of your vertebra and causes pain (usually because your spinal nerves/spinal cord are under pressure because of deformation).  such deformation can also be caused by obesity. so, if you have a big belley hanging down, it's time to start losing weight.

check for possibilities of other diseases like osteoporosis; we tend to neglect diet since we are too busy with school and/or work. but this negligence is affecting you, slowly but surely. it's just the matter of time when symptoms start to appear. you working at gas station could be totally unrelated to your back pain.