Thank you for your question.
The mere fact that it has been happening for such a long time will exclude dangerous conditions, for they would have become a lot more severe over a shorter time period. This might be an abdominal muscle injury
or an intra abdominal organ problem, because of the association with movement. I suggest that an abdominal ultrasound
should help with the diagnosis, seeing as this is such a chronic problem , have a doctor diagnose the problem.
Please feel free to ask for any further help.