Problems with breathing caused by breathing exercises

About a year ago, I started doing these breathing exercises that I read about online (can't find the link though). It was basically just taking short, quick breaths but following the breath all the way through so your chest expands. However, I think my lungs were damaged by it. Since I stopped doing the breathing exercises, my lungs have this closed up feeling and sometimes I have to take a slow deep breath to counter the feeling. Also, ever since, I also randomly, get sharp darts of pain that last for a second or so, just below my left rib-cage. Does anyone have any idea of what went wrong or what I should do?