Hi, I Have Been Having Some Chest Discomfort. It Feels

hi, i have been having some chest discomfort. it feels a little like my heart is quivering or vibrating. i have been to the ER twice and my pcp twice BUT all my vitals came back good, my EKG was good. i was diagnosed with costochondritis but i just feel like it might be something more and was looking for another opinion. i am 21 years old. no medical history really, blood clots in the family. i had blood drawn for a clot test and it came back abnormal, so i was scanned to check and be sure it wasnt near my heart or lungs. i just need my mind put to ease.