How to gain weight?

Im 14 years old, and I really need some help from all of you. I know lot of people have asked this before, but I'm going to do the same thing cause I have the same problem.
Im thin. Really thin for someone of my age. (14) When people see me they say "omg how thin (skinny) you are!" That really hurts. I eat a lot almost every day and nothin. I have a very fast metabolism. Is there anything I can do to slow it down? When people see me they think I am thin cause I dont eat anything but I really do. I really need to gain weight as fast as I can. Mostly 3 months. I am 35kg how freaky is that? What food has lot of calories, and makes you gain lots of weight. If you know any trick that makes you gain weight fast please tell me.
Thank you!
Thank you

Hi gaining lots of weight by eating high calorie foods will just eventualy make you fat.I think what you should do is start adding muscules! low fat high protein meals carbs and so on.get into sports!!just don't over do things you can't go from 35kg to whatever your goal is overnight.

to calculate your bmi (body max index) wed need to knwo your height
but at 35kgs you should weight at least another 10, even with the fast metabolism
to gain weigth you also need to do it healthily
so dont just go eating all the junk food you can!
theres also no way to change your metabolism, its pretty much set by your body
increase your daily calorie intake,
add more fatty foods but also eat stuff thats good for you
also if you do too much physical activity,
like sport or exerscise youll need to slow that down a lot to gain weight
you could also try checking out a pharmacy and see if they have any food or bars that help you gain weight
because just like weight loss things, theres also things for weight gain

Great and Healthy Plan: http://www.mayoclinic.com/health/underweight/AN00597

Yes I do want to gain about 10kg...

Weight lifting will cause you to gain weight. Muscle weighs more than fat. If it was me, I would stay away from cardio workouts though as they burn fat but do not build muscle.

Have you talked to your doctor yet? He/she may have some ideas on how to gain some weight. Also, some health food stores have weight gain powders that have helped other people gain weight. I had a friend that was really thin like you and she did the powder/shake thing and actually was able to gain some weight and get to a healthy size.