What to do for rapid heart rate!!!?

Im 18 years old..not overweight at all. I eat okay and i exercise daily. I was diagnosed with High blood pressure and rapid heart rate. The doctors think that the hbp comes from my rapid heart rate tho. I have had numerous EK G's and they all have came back wrong so I wore a 24 hour halter Monitor and also had an ultra sound of my heart as well. It showed that I had mitral valve prolapse and I had to end up wearing a 21 day halter monitor. The doc said that my medicine mainly kept my heart rate down but it doesn't all the time. I am currently taking Metoprolol tart 50 mg. Even thought I am on this i am still experiencing the rapid heart rate badly. It stays over 100 beats a minute and resting sometimes goes to 150-160 a minute. When my heart beats fast I get nauseous, really hot, dizzy and i have even ped out....i need to know what to do...go back to doctor or just deal with it?