Several heart palpitations a year with nausea lasting for several hours each after exercise, echo and holter tests found nothing, what should I do?

Need evaluation. I assume by your question, that the holter was done while feeling the palpitations? If so, and no rhythm problems were found, the palpitations are probably nothing to worry about, if, however, you did not have symptoms while monitored, it could still be undiagnosed arrhythmia. Start by decreasing intensity of exercise, and consult a physician (start with primary care, or choose cardiolgist).