Hi
Welcome to the forum!
Pain in the upper left abdomen and chest area can be due to stomach issues, spleen issues, due to an abscess below the left diaphragm, a hematoma (localized collection of blood), an abscess, or a muscle pull (as it happened while playing). Ultrasound would have ruled out spleen problems and an abscess below the left diaphragm. A CT scan would be more diagnostic.
The chances of it being a muscle pull are very high. It could also be an abscess or infection in the skin or muscle layer. A clinician can examine and tell if it is either of these.
I think you should discuss these possibilities with your doctor (PCP) and get a referral for a sports clinic and consult a sports medicine specialist. It is difficult to comment beyond this without examining.
Hope this helps. Please let me know if there is any thing else and do keep me posted. Take care!
Did they also look for an endometrioma? Did they suggest a hemoccult test (stool)?