hi, i was in a similar situation a few years back, needless to say i ended up calling people at 4am to bring me to the hospital many times, each time they found nothing. this was very frustrating to me. it turned out i was suffering from anxiety and hyper tension (every time the palpitations came they came with severe chest pain and i thought it was a heart attack) well anyway i tried anti anxiety medication for a while and it seemed to help, it doesnt bother me anymore because i now know it was harmless but at the time it was hell. But i do think you were treated poorly and doctors really should know better !!!
anyway i hope you find some answers soon and my best wishes to you