I'm pretty sure you won't lose 10 pounds every day until you die. If it's fluctuating, then you just have the metabolism of an 18 year old. I used to wake up 5 pounds lighter than the day before and it was the day after Thanksgiving. It's ridiculous. As long as you're eating plenty and being healthy, you should be fine.
No, assuming that you don't have an eating disorder, this is not normal unless you retain a lot of fluid, which you shouldn't, at your age ......... It sounds like you could be suffering from an overactive thyroid; have you ever had thyroid function tested? Get the following tests: TSH, Free T3 and Free T4, plus TSI; and get checked for Type I diabetes........ these are 2 major health issues that cause weight loss....... don't panic, but get tested for both asap....