For the past year or so I have been getting a stabbing pain in my heart. And at random my heart will beat faster or will slow down and will beat hard for a few beats. I do have anemia, and when I was little(1-4 years of age) the doctors said i had a heart murmur. I'm 16, 5'2" 95-103lb(my weight changes alot) I don't get stressed that often I do work out. And so I was wondering if i should be worried and is there any heart diseases that I could have.