That depends. Are you a girl? I only know that girls' weights can fluctuate a lot especially because of water retention due to our period. Not normally 10 pounds in 4 days but you never can tell when you're dealing with hormones. Did you eat a lot during those 4 days? Did you use different scales? There are many factors. You could very well be...um...how to put this?...constipated. If that's the case and you haven't...well, you know... in a while, get more fiber into your diet with apples and Fiber 1 cereal . That said, random teens on the Internet are no replacement for a real diagnosis, prognosis, whatever. You may want to consult a doctor if there have been no significant changes in your diet, and especially if your stomach has been hurting.
Just because everything's changing
Doesn't mean it's never been this way before
All you can do is try to know who your friends are...