Pringle, your age has very little to do with what you should weigh; your height and bone structure do. Add to that the fact that you are still growing and maturing and you are dangerously underweight already if you are truly 5' 8" tall. Your goal weight is only 15 pounds higher than what my 9 year old daughter currently weighs. She is ranked in the 50th percentile for a girl her height (in other words, exactly what she should weigh) and she is 15 inches shorter than you!
I strongly encourage you to see a doctor before you try to lose more weight and follow that doctor's advice. I am very concerned for your current and future health and wellbeing.