My life is going by so fast?

Ok, so I'm 15, and I'm going to be a sophomore this year, and lately i've just been feeling really weird. It started when me and my family went on vacation to a place where we always used to go when I was little, and I saw all these things and places that brought back so many memories from when I was little, and it felt like they were just last year. I wish i could go back to being a little girl awho gave her mommy and daddy hugs all the time and played with stuffed animals and didn't care about anything else. i know im still only 15 and i have my whole life ahead of me, but its just going by too fast. i keep thinking about how my freshman year went by so fast, and in 3 years im gonna graduate and im gonna be on my own, and im never ever gonna be that little girl again, and it just makes me so sad because i want to go back to that. it just makes me so sad, i'm bawling my eyes out right now because i just miss it and i dont want my life to just fly by. how can i try to stop feeling so depressed about this?? please help me, i really appreciate it.