My daughter is 21 years old and has had chest tightness and left sided discomfort under her ribs that now feels like something is crawling in her rib ?

Odd symptoms: Given the age,location & description the most likely origin is from the end of her swallow tube as it enters the stomach. This is just behind the heart. Stomach acid backwash can easily trigger stabbing or gnawing pain & the stomach muscle squeezes the contents to mix its contents.(producing movement) Avoiding caffeine, nicotine or lying down after meals can help. Using an acid reducer helps also

Doctor can examine: Chest tightness or shortness of breath is not normal, unless it is the mild temporary shortness of breath with sports activities (but even then, one must be sure she is not having more shortness of breath than her sports peers have). Possible reasons for symptoms include lung or heart disease, fluid or irritation of the linings of the lungs or heart, acid reflux, asthma, anxiety, costochondritis, etc.