What Causes Elevated Resting Heart Rate And Sharp Chest Pain?

Hello my name is emily. I am a 22 year old female and in the last year my resting heaet rate has sky rocketed from a normal 60 bpm to now my resting heart rate is usually 115bpm thats resting. I can sometimes hear my heart beat in my head and it sounds like its going to explode I even get sudden sharp stabbing pains where my heart is sometimes. I used to be a gymnast for 15 years and I am very healthy and active. What would cause such a rise in my heart rate?