I feel very weak(What could be wrong)?

I am eating enough. I am getting enough sleep right now. (Even more than enough) and I am still tired. My body feels weary. I went to the doctor's and I had tests on my heart and the results have not come in yet. I am about 112 pounds and 4'11. Could it be because too much for my height? I am freaked out that there could be something wrong with my heart. I am only 17.