I am 17 years old. And I just had a dr. appt today and they said I weigh 86 1/2 pounds.
I don't think this is right because I eat an actual meal for lunch and dinner [i don't have time for an actual breakfast so usually I get chips or something]] and I always have little snacks in between all those times. I am not anorexic or bulimic. And I don't have a lot of stress and I get at least 7 hours of sleep every night. Other people say I have a fast metabolism. I always have.. but.. I don't see how I can weigh 86 pounds though.. one of my friends mom has this disease? Where she can't gain weight no matter what. She is stick skinny and very bony. She eats probably as much as I do and she weighs in her 80's and she is over 50 maybe? Could I possibly have that? What could be making me lose all this weight?

İf you eat a lot or eat normal and still can't gain weight it would be okay but if you are 'losing' weight I have only one thing to say: RUSH TO A DOCTOR!

I was just like that.. I'm 19 now and I've started to gain weight..
You're friends mom probably has an overactive thyroid.. which doesn't allow you to gain weight easily.. Ask your friend if his/her mom has an overactive thyroid problem. If she does, talk to her about it.. or you could go to the doctor if you are really concerned that you have this.. (I really know nothing about this disease other than an if you have an overactive one.. its hard to gain weight.. and if you have an underactive one.. you pack on lots of weight)
Other than that.. just eat healthy and you'll be fine.. you'll start to gain more weight in the next few years.

I also have a 17 year old son who can't gain weight. He like you eats lots of chips.and can have up to 7 packets of crisps a day. I've taken him to my doctor. But have been told his fit and well. I really wouldn't worry. Count yourselves lucky as you guys can eat what you want.