For your height, and age, you should weigh probably around 100 pounds. At this age, your body will be changing almost daily, and you can expect weight change as well. But, I feel that anywhere between 100 and 110 should be OK. If in doubt, ask a nurse or doctor.
I saw this chart, maybe it will help:
Height and Weights for Teen Girls
Age Range Height Weight Percentile
12-13 years 60 – 63 inches 95 – 105 lbs 50%
14-15 years 63 – 64 inches 105 – 115 lbs 50%
16-17 years 64 inches 115 – 120 lbs 50%
18-20 years 64 inches 125 – 130 lbs 50%
Everyone is different, if you have a small frame, then your weight should be lower, if a medium frame, a little higher, and for a larger frame higher yet.
There is no fast way to slim down, and the ones that claim to be fast are NOT healthy. The best way is slow and steady. Eat smaller, but healthier meals, cut out all sugars and desserts, drink at least 8 ounces of water 8 times a day, and be sure to exercise daily. A good, brisk, 45 minute walk it great, and it also helps you to feel better in general. Also, do NOT skip breakfast, if you do, you will be hungry all day, eat a healthy breakfast and this will set you up for the rest of the day and you won't be starving and over-eat at any meals.
Good luck, please keep us posted as to your results.