Now pain on the left side of the chest always has to be considered as related to the heart until proved otherwise. Even though your age is not consistent with that of heart disease, but pain which occurs in the chest should be evaluated with the help of a simple EKG. Especially if it is accompanied by sweating, radiation of pain into the arm or jaw, nausea, vomiting etc. I would recommend that even though i think it is less likely to be due to heart disease, you should have this pain evaluated at your ER. Sometimes pain in the chest related to the heart can occur without the other symptoms.
Now what this is more likely to be is either a musculoskeletal problem or related to the lungs. i think it is likely to be acute costochondritis which is a condition in which there is inflammation of the cartilages of the ribs. This can cause pain in this region which can worsen on deep breathing and also cause tendernes sin the region. if this is the case then you can have this diagnosed via a simple clinical examination after which it can be treated with OTC drugs like motrin or aleve (however in your case topical voltaren gel would be better along with tylenol because of the gastric sleeve).
Another cause of this can be related to the lung, sometimes the covering of the lungs can be inflammed which can lead to pain in the chest which worsens on breathing. This can also cause coughing or shortness of breath in some cases. The diagnosis is made with a chest xray and then treated with simple antibiotics in most cases alongwith steroids.
Now i would suggest that you use OTC tylenol for the pain but do get the EKG done even though the chances of heart diseae are low, it is best to rule out the heart in situations like these.
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