My 14 year old daughter have a bothering pain on the left side of her abdomen like under the rib cage, she says is not too painful but when she take deep breaths or yawn she feel it more. she says it feels like gas or muscle pain. what can it be?

Gas or muscle pain or something else. The location is where the large intestine drops down after crossing under the breathing muscle. It is a common place for gut gas to accumulate in some. Having the kid lay down with pelvis/feet above the head can get the gas to move lower & out if that is the case. Vague symptoms often have more than one possible source.