ipod constantly freezes and shuts off randomly.

i've had my iPod 5 for about a year and half and do use it a lot but within the past 5 month time frame, its been freezing and shutting off. theres times like right now where it shuts off completely and when i get it back on, all my messages are gone. My home button is stuck so i can't hold it down to reset it. I let the battery drain but it still doesn't work. its so frustrating. i tried plugging it into my mac and it doesn't even recognize my device. Ive been to the apple store many times and when i go it just so happens to turn on when i walk into the store. please help!!!