How much should a 14 year old girl weigh?

Hi everyone says I'm to skinny. I am 5ft 3in, I currently weigh 86lb. I've never been over 100lb. The most I've ever weighed has been 95. Am I to skinny? How do I gain weight if I am? I eat more than normal servings. I usually am able to double it. But I work outside with my animals.