I Am Experiencing Palpitations, Please Help Me

Hi I am 19 years old and experiencing problems with heart palpitations. I am in college, married and under a TON of stress right now with classes, assignments and work. I am seeing a cardiologist about my palpitations and they say there is nothing phsycially wrong with my heart. I have had a chest x-ray , several EKGS, the 24 hr holter monitor twice and an echo. They say that is nothing wrong with any of my valves and my heart function is normal, so my question is why does my heart palpitations keep happening? The cardiologist did say that my heart was a little fast for my age, but for the most part my blood pressure has been pretty good. I am a little overweight and hardly ever exercise, my diet consists of a lot of junk food. If you have any answers for me please let me know, I am driving myslef crazy with worry. I have been dealing with this for a while so any answers would help me out.