What Could Cause Persistent Chest Discomfort, Feelings Of Shortness Of Breath, And Intermittent Chest Pains In A Healthy Young Adult?

Im young, 25 and been having weird problems for a couple years now. I feel a strange feeling in my whole chest and i been to the doctor for it before and my breathing is normal but it gives me a feeling that im shortness of breathe and slight pains in all different areas of my chest at different times and i feel this way 24/7. im fit and healthy, do alot of heavy lifting outside for work also. it usually goes away after about 3-4 weeks but i worry every time it happens