Starting last June I started to feel tired and had a rapid heartbeat so I stopped exercising and took it easy. When I still felt bad in mid July, I went to my doctor and she said I was dehydrated. I already drink a normal amount of water but then I was really on top of it. In August, my soccer season started and I still felt tired all of the time and had a rapid heart beat. Even after going up the stairs I would be out of breath. I went to a cardiologist and she said I was just dehydrated. I kept drinking plenty of water but I still felt awful. By mid October, I was done with soccer. Finally, in November, I got blood tested and was told that I had mono. Now, it's December and I don't feel any better. Should I be concerned that this is more than just mono?