I Have Headaches, Nauseousness, Faintness. What Could Be The Reason?

I often feel like my heart is beating either extremely fast or slow (I checked my pulse once and it was really slow) I get head aches that are similar to migranes, sometimes I feel like fainting , and I often feel nauseous. I am the MVP of my school s wrestling team so i wouldn t think of my self as having a weak or frail body. I m 15 this has been going on for a few years but my parents don t believe me. Any ideas? I wrestle at a wheight class higher than mine so i don t have to starve myself so make the weight cut off. I wrestle at a wheight class higher than mine so i don t have to starve myself to make the weight cut off.