How can I prevent my ipod touch 5 from resetting itself frequently?

I got my iPod touch 5th generation in March of 2014. It updated all the way to ios 9 but has not updated since. Now, it shuts down and turns on without any warning. It will also constantly freeze. It's gotten to the point where I can't do two things at once(listen to music and play a game). Does anyone have any solution for this? Also, my iPod has recently completely reset itself as if I had just bought it from the store. I haven't had a chance to see how I can fix this but it has happened once before. How can I prevent this from happening again without buying a completely new iPod or phone?