If you're really worried, get an x-ray of the location where you have the back pain. If nothing comes up, then it means your posture is shit or you just have general tightness in the soft tissue in that area. For both, going to the gym putting on muscle and increasing your strength will help quite a bit. Stretching will also help. Additionally, going to a masseuse will help.
2 of the vertebrae in my lower back have been fucked, presumably since birth. They're expected to degenerate significantly faster, but that notwithstanding, the bony spurs dig out, so when you put pressure in that area, even mild pressure, there is excruciating pain. Found out due to an x-ray, although I was complaining about pain since 8-9. When I started going to the gym, alongside going to a masseuse from time to time, the pain in that area subsided, as well as the swelling in my lower-back.