What is this chest pain?

Im 18 years old. Since the age of 15 I ve been having sharp chest pains, usually on the left side of my chest. What is the world is this? Im frustrated because i have been to a doctor about it. When i was 16/17 I wen to the ER and got a EKG of my heart , some blood tests (general), ultrasound of the stomach area and a urine ysis (glucose etc.) It all came back clean. The doctor told me I was very young and healthy. I the time I had been experienceing severe stress. Bu the thing is it is still not gone. I still, maybe once a day for 2-4 seconds get this weird sparp pains on my left side. I have notince that they occur with change in position. I touch the rib at the area of the pain and I can feel more pain. A month ago I started to feel like i could not breathe properly. It is weird because like my mind tells me nothing is wrong. I check my breathing rate and its normal but some how i panick and begin to breath faster when not needed. I also feel like Im sort of outside my body at times. Like my mody has no weight and im floating. It is preatty crazy, because it is like I do it to myself. I remember that feeling and my mind ends up convincing my body to feel that hard breathing floating feeling. It starts with like a ( to relate) umm..when a person suddenly gets scared like (BOOM!) and you heart feels like it just SANK deeper into you chest. That is how it starts. Is this a panick attack? I m not going to the doctor anymore because my parents and the doctor told me already that im 100% healthy. Anyone else with this problem? SORRY FOR THE TYPOS