Why am I feeling depressed about good memories?

all of a sudden, things just started to hit me constantly. everywhere i go, something reminds me of memories i used to have. good or bad, i still miss them, and inside of me i feel this huge emptiness. it feels as if i'm homesick, even though i am at home and i don't understand what it is. sometimes i find myself hurting inside so bad about old times i feel like crying. nothing really happened for me to miss those times so much, but i just do. even though my life has drastically changed over the course of a year, i don't really think it was for the worse. but i feel like i need someone to talk to because no one is there for me. i feel as if things were better as a child because i had much less trouble with my family. perhaps, the fact that i can't communicate with my parents is driving me to depression? i honestly never felt this empty in my life. as if i need to get away somewhere and re-live all the memories. i feel like, right now, i'm being held in a prison and having a big brick weighed on my wooden twig body until i snap and collapse (figuratively). what is this?