Can a heart murmur cause fatigue, throwing up heart pounding very fast for a 5 y/o about once a month. doctor says they can't find anything wrong.

Possibly & unusual: If you have not had your child evaluated by a pediatric cardiologist, ideally at a children's hospital, such as in oakland or san francisco, it is worth setting up the evaluation by an expert for both a second opinion and an expert opinion, to see if anything is being overlooked.

Not usually: A heart murmur is just a sound in the heart, can be caused by many things, but also can be an innocent murmur (meaning that the heart is normal and the murmur is just sound of blood moving in a normal heart). So, if the cardiologist told you the heart is structurally normal, then an innocent heart murmur would not cause the above symptoms. Recommend seeing a peds. Cardiologist.