My imessage logged me out and now won't let me log back in, what do i do?

My imessage has been logging me out recently, so i have had to log back in. But this morning I went onto the app and it had logged me out, so when I tried to log back in it says that i need to connect to a service, but i am connected to the internet and its working fine. I even changed my password to see if i was typing it in wrong and it still isn't letting me log in... What should I do?

My device is an iPod 5th Generation.