I think you need to see a cardiologist who specializes only in the treatment of cardiac arrhythmias. Cardiology, like most medical areas, is also highly specialized. You are describing an arrhythmia--a disturbance in the normal rhythm of the heart--because you are experiencing palpitations. You also know that your heartbeat is too fast. These problems need to be further evaluated, and an arrhythmia cardiologist is the person who will know which are the best diagnostic measures to employ.
You can read more about cardiac arrhythmias here
Your symptoms might be caused by other factors, besides cardiac problems, but I think it is important to rule out all cardiac issues first, before exploring other possible causes, because these can be the most potentially life-threatening.
Your symptoms are quite similar to those experienced by my mother. My mother has both angina and a cardiac arrhythmia (she has atrial fibrillation) and her symptoms (particularly the palpitations) proved somewhat elusive to track down. Whenever she wore a Holter monitor, her symptoms did not appear. In fact, we joked that the solution to her problem was simply to wear the monitor all the time.
But her doctors were still able to get the problems under fairly good control with appropriate medications.
Several years ago, my mother suddenly developed a problem with bradycardia--she had episodes where her heartbeat would slow down (to about 35 beats per minute), and this would last for a day or two and then her heartbeat would return to normal. She again consulted an arrhythmia specialist who did an electrophysiologic study to evaluate her for a pacemaker. He found she did not need a pacemaker, but he discovered that she had an extra node in her heart which could make the heartbeat speed up and cause tachycardia, or rapid heartbeat. During the test he ablated (removed) this node, and since that time, she has not experienced any significant or unpleasant episodes of rapid heartbeat. Mysteriously, her episodes of too slow heartbeat also ceased after this procedure was done.
So, even with cardiac rhythm problems, symptoms can be effectively addressed and treated, and the diagnostic tests are really not unduly unpleasant. But I would urge you to see an arrhythmia specialist, if possible, since different types of cardiologists specialize in treating different types of problems.
You might also consider consulting an endocrinologist to more systematically evaluate your problems with blood sugar fluctuation. Also, some electrolyte imbalances can affect heart rate and heart rhythms, and an endocrinologist would be the best medical specialist to investigate those possibilities.
I hope you are able to get your problems properly diagnosed and treated soon. In the meantime, do something simple, like eliminating caffeine from your diet. Don't drink coffee or cola drinks, and even watch your intake of chocolate. Caffeine can certainly contribute to an increased heart rate.