Upset Stomach, Belching, Nausea, fatigue and Tight Sternum... during Exercise

This is really holding me back, i've had this problem for a while and i don't know exactly what it is. I even ate vegetables and still seem to be affected. My doctor did a blood test and came up with "i'm fine". I've tried candida treatments but still have no energy. It's quite strange and is really affecting my athletic performance. I find it hard to breath because of my tight sternum, i belch, feel dizzy when running, lack of energy and my stomach feels uneasy.. can you help? Tweet