Brief Answer:
COnsult a physician to pin point the cause & needful treatment

Detailed Answer:
Hi XXXX,
Thanks for the query. The pain seems to be disturbing. Such stitch like sudden pain coming off & on without any abnormal findings in USG can be from-
- A muscle pull, occurring after physical stress & can be avoided by proper warming up before starting exercises. / a compressed nerve by spinal or disc problem or/ fractured rib - causing irritation of muscle in certain posture of body.
- A psychological stress can lead to problem in food digestion , bloating & stitch like pain i under rib cage/ anxiety itself can cause muscle spasm & pain/ Irritable bowel syndrome can cause such stress induced pain.
-Rarely it can be from heart , spleen or kidney involvement.
* Management- Most of the times pain subsides after some time..but It's not advisable to neglect certain possibilities & also looking at it's persistence over a long period of 3 years I would suggest a Physician's consultation . Get a through physical examination & investigations to pin point the cause & exclude more serious causes like heart problem .
Treatment would be cause specific ranging from simple life style changes, stress management , physiotherapy, or specific medications as per expert advise.
I hope the answer was informative & useful to you. Any follow up query is welcome.
Thanks.

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