Heart racing problem, EKG doesn't show anything. Put on beta blockers, still heart races. What to do ?

my name is AAAAA , I m 23 years of age. actively fit and in good shape. over the years i have had heart racing problems and doctors have determined it anxiety have done a ekg holder monitor and nothing ever shows up. but lately it has been worse. the most serious one was at about 240bmp and had to go to the er. as soon as i got to the hospital it stopped just as fast as it started. so i went to see a cardiologist at mercy medical in sioux city ia. they put a luper monitor in my chest(sorry on the spelling) so they can record the activity. i have had it in for about 3 weeks now and have had more than 4 episodes of the heart racing very fast and sent in my recordings. she put me on some beta blockers to slow the rate down. and i just started taking it today and when i took it this morning, ten min later my heart started racing like crazy. i just want an answer and a fix to this problem. i want to go back to my normal life without having to worry I m going to die every time this happens. if you could please help me out that would be greatly appreciated!