Brief Answer:
Costochondritis or gall bladder pathology

Detailed Answer:
Hi.
Thanks for your query, albeit short and specific.
The commonest causes of sharp pain under lower right side of the rib are:
Costochondritis
Gall bladder inflammation.
Liver pathology, although rare to cause sharp pains.

Watch for the following symptoms and signs:
If there is tenderness on pressure over the lower rib the most probable cause can be costochondritis.
If the pain is below the ribs, referred to back or right shoulder and increase on deep palpation or deep breathing, it may be gall bladder inflammation.

This can be confirmed by local palpation, palpation with deep breathing.
Ultrasonography of abdomen.
Relevant tests of blood like liver function test.
Clinical evaluation and examination by a Doctor, preferable a General surgeon.
Earlier the diagnosis better is the management and outcome.

I hope this answer helps you, please feel free to give feedback and ask for further relevant queries if you feel that there is a gap of communication.

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