Chronic pain in left part of the abdomen

Dear experts,
I have been facing a long standing pain in the left part of my abdomen. I have gone through many physical checkup but nothing was found. It went on for over 10 years. Finally, i came to realize it's it has a connection with quantity and quality of sleep, stress, mental soundness etc. When i have no stress and sleep well, i don't feel the pain. But when i go through a stressful day and can't sleep well at night, the pain comes back. Any advice would be much appreciated.