Is weight okay for a small 13 year old

I'm a 13 year old girl and I weigh only 5 and a half stone. Is this alright? I'm definitely small for my age and I have a problem where I eat loads, but don't gain weight! Thanks

whats 5 and a half stones? lol sorry.
and sometimes it is just thank you are really active and your body uses it before it could be used as a type of body fat, your best bet is to eat things with protine and do eat a lot of junk food, I am the same way im 17 and only weigh 100 pounds

You're definitely small, 77 pounds is small. You've probably just got a really fast metabolism. If your doctor says you're healthy otherwise, I wouldnt worry about it.