What can I do about abdominal pain that is a side affect of prevacid?

I play lacrosse and ever since I have been taking prevacid I have been getting abdominal pains when we run. It does not take much running at all. Each lap is around two fields, when we do two laps I cannot even move it is so painful. I don't know what to do about it becasue if I don't take the medicine then I cannot breathe. The abdominal pains are only on the right side and upper and lower. At first I thought it was because I was not eating at all before but now I am eating and they are still there. I have lost ten pounds in the last week as well. I haven't been eating much and I don't know if that has anything to do with it.