Scotty, I asked myself this question when I was about 15! I was about your height. I am now 5'7" as an adult. one of my brothers is 6'4". another is over 6' tall. you may not have reached that growth spurt yet! in any event, be content in the person you are. you are unique! among 7 billion people on this crazy planet, there is only one "you!" and you are awesome! I hope my answer doesn't sound sorta lame. it's the best I have. stay safe and celebrate life...;-)
it has to do with genes, my friend has curly brown hair and both his parents have straight blonde hair. genes are strange and can be passed though many generations, it is possible that you got a gene from one of your parents that they got from their parents that was just not a dominant gene and so your parents may be tall and you be short.
Maybe you're still growing and need to be patient, or, maybe you just got the...wait for it....short end of the genetics stick! Lol sorry, as a fellow short person with tall siblings I had to throw that in there. XD